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1. Return values None 4 3 Legacy API 73 PyVISA Documentation Release 1 5 get_attribute Retrieve the state of an attribute Call attribute_state get_attribute vi attribute VISA name viGetAttribute Parameters vi integer ViEvent or ViFindList Unique logical identifier to a session attribute integer Session event or find list attribute for which the state query is made Return values attribute_state integer string or list of integers The state of the queried attribute for a specified resource gpib_command Write GPIB command bytes on the bus Call return_count gpib_command vi buffer VISA name viGpibCommand Parameters vi integer Unique logical identifier to a session buffer string Buffer containing valid GPIB commands Return values return_count integer Number of bytes actually transferred gpib_control_atn Controls the state of the GPIB ATN interface line and optionally the active controller state of the local interface board Call gpib_control_atn vi mode VISA name viGpibControlATN Parameters vi integer Unique logical identifier to a session mode integer Specifies the state of the ATN line and optionally the local active controller state See the Description section for actual values Return values None gpib_control_ren Controls the state of the GPIB REN interface line and optionally the remote local state of the device Call gpib_control_ren vi mode VISA name viGpib
2. VISA name viMove Parameters vi integer Unique logical identifier to a session source_space integer Specifies the address space of the source source_offset integer Offset in bytes of the starting address or register from which to read source_width integer Specifies the data width of the source destination_space integer Specifies the address space of the destination destination_offset integer Offset in bytes of the starting address or register to which to write destination_width integer Specifies the data width of the destination 78 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 length integer Number of elements to transfer where the data width of the elements to transfer is identical to source data width Return values None move_asynchronously Move a block of data asynchronously Call job_id move_asynchronously vi source_space source_offset source_width destination_space destination_offset destination_width length VISA name viMoveAsync Parameters vi integer Unique logical identifier to a session source_space integer Specifies the address space of the source source_offset integer Offset in bytes of the starting address or register from which to read source_width integer Specifies the data width of the source destination_space integer Specifies the address space of the destination destination_offset integer Offset in bytes of the starting address or register to w
3. Value Description last_bit_end_input read will terminate as soon as a character arrives with its last data bit set term_chars_end_input read will terminate as soon as the last character of term_chars is received The default value is term_chars_end_input 2 6 Architecture PyVISA implements convenient and Pythonic programming in three layers 1 Low level A wrapper around the shared visa library The wrapper defines the argument types and response types of each function as well as the conversions between Python objects and foreign types You will normally not need to access these functions directly If you do it probably means that we need to improve layer 2 2 Middle level A wrapping Python function for each function of the shared visa library These functions call the low level functions adding some code to deal with type conversions for functions that return values by reference These functions also have comprehensive and Python friendly documentation You only need to access this layer if you want to control certain specific aspects of the VISA library such as memory moving 3 High level An object oriented layer It exposes all functionality using three main clases VisaLibrary ResourceManager and Instrument It is important to notice that you do not need to import functions from levels 1 and 2 but you can call them directly from the the VisaLibrary object Indeed all level 1 functions are static methods of Vi
4. to this property the termination sequence is deleted The default is None which means that CR LF is appended to each write operation but not expected after each read operation but stripped if present 40 Chapter 3 More information PyVISA Documentation Release 1 5 trigger Sends a software trigger to the device write message termination None encoding None Write a string message to the device The term_chars are appended to it unless they are already Parameters message unicode Py2 or str Py3 the message to be sent Returns number of bytes written Return type int write_raw message Write a string message to the device The term_chars are appended to it unless they are already Parameters message bytes the message to be sent Returns number of bytes written Return type int write termination Writer termination character class pyvisa highlevel SerialInstrument resource_name resource_manager None keyw Class for serial RS232 or parallel port instruments Not USB This class extents the Instrument class with special operations and properties of serial instruments Parameters resource_name the instrument s resource name or an alias may be taken from the list from list_resources method from a ResourceManager Further keyword arguments are passed to the constructor of class Instrument baud_rate The baud rate of the serial instrument data_bits Number of data bit
5. Maps the specified memory space into the process s address space Parameters library the visa library wrapped by ctypes session Unique logical identifier to a session map_space Specifies the address space to map Constants SPACE map_base Offset in bytes of the memory to be mapped map_size Amount of memory to map in bytes access suggested If not Constants NULL 0 the operating system attempts to map the memory to the address specified in suggested There is no guarantee however that the memory will be mapped to that address This operation may map the memory into an address region different from suggested Returns Address in your process space where the memory was mapped pyvisa ctwrapper functions map_trigger library session trigger_source trigger_destination mode Map the specified trigger source line to the specified destination line 3 4 API 47 PyVISA Documentation Release 1 5 Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e trigger_source Source line from which to map Constants TRIG e trigger_destination Destination line to which to map Constants TRIG mode pyvisa ctwrapper functions memory_allocation library session size extended False Allocates memory from a resource s memory region Parameters e library the visa library wrapped by ctypes e sessio
6. buffer_write Similar to write except the data is written to the formatted I O write buffer rather than directly to the device Call return_count buffer_write vi buffer VISA name viBufWrite Parameters vi integer Unique logical identifier to a session buffer string The data block to be sent to device Return values return_count integer The number of bytes actually transferred clear Clear a device Call clear vi VISA name viClear Parameters vi integer Unique logical identifier to a session Return values None close Close the specified session event or find list Call close vi VISA name viClose Parameters vi integer ViEvent or ViFindList Unique logical identifier to a session event or find list Return values None 4 3 Legacy API 71 PyVISA Documentation Release 1 5 disable event Disable notification of an event type by the specified mechanisms Call disable_event vi event_type mechanism VISA name viDisableEvent Parameters vi integer Unique logical identifier to a session event_type integer Logical event identifier mechanism integer Specifies event handling mechanisms to be disabled The queuing mechanism is disabled by specifying VI_QUEUE and the callback mechanism is disabled by specifying VI_HNDLR or VI_SUSPEND_HNDLR It is possible to disable both mechanisms simultane ously by specifying VI_ALL_MECH Return values None discard_events
7. from pyvisa legacy import visa itc4 visa instrument COM2 print itc4 ask V It couldn t be simpler See section Serial devices for further information about serial devices 4 1 3 A more complex example The following example shows how to use SCPI commands with a Keithley 2000 multimeter in order to measure 10 voltages After having read them the program calculates the average voltage and prints it on the screen Pll explain the program step by step First we have to initialise the instrument from pyvisa legacy import visa keithley visa instrument GPIB 12 keithley write xrst status preset x cls 60 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 Here we create the instrument variable keithley which is used for all further operations on the instrument Immediately after it we send the initialisation and reset message to the instrument The next step is to write all the measurement parameters in particular the interval time 500ms and the number of readings 10 to the instrument I won t explain it in detail Have a look at an SCPI and or Keithley 2000 manual interval_in_ms 500 number_of_readings 10 keithley write status measurement enable 512 xsre 1 keithley write sample count d number_of_readings keithley write trigger source bus keithley write trigger delay 3f interval_in_ms 1000 0 o keithley write trace points td number_of_readin
8. pyvisa ctwrapper functions read asynchronously library session count Reads data from device or interface asynchronously Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e count Number of bytes to be read Returns ctypes buffer with result jobid pyvisa ctwrapper functions read_to_file library session filename count Read data synchronously and store the transferred data in a file Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session filename Name of file to which data will be written e count Number of bytes to be read Returns Number of bytes actually transferred pyvisa ctwrapper functions read_stb library session Reads a status byte of the service request Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session Returns Service request status byte pyvisa ctwrapper functions set_attribute library session attribute attribute_state Sets the state of an attribute Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session attribute Attribute for which the state is to be modified Attributes attribute_state The state of the attribute to be set for the specified object pyvisa ctwrapper functions set_buffer library session mask size
9. Writes data to device or interface synchronously Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e data str data to be written Returns Number of bytes actually transferred pyvisa ctwrapper functions write_asynchronously library session data Writes data to device or interface asynchronously Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e data data to be written Returns Job ID of this asynchronous write operation pyvisa ctwrapper functions write_from_file library session filename count Take data from a file and write it out synchronously Parameters e library the visa library wrapped by ctypes session Unique logical identifier to a session e filename Name of file from which data will be read e count Number of bytes to be written Returns Number of bytes actually transferred 3 4 API 57 PyVISA Documentation Release 1 5 58 Chapter 3 More information CHAPTER 4 Legacy Modules Note This is a legacy module kept for backwards compatiblity with PyVISA lt 1 5 and will be deprecated in future versions of PyVISA You are strongly encouraged to switch to the new implementation 4 1 About the legacy visa module Abstract PyVISA enables you to control your measurement and test equipment digital multimeters motors
10. e session Unique logical identifier to a session e event_type Logical event identifier e mechanism Specifies event handling mechanisms to be disabled Constants QUEUE Handler SUSPEND_HNDLR e context pyvisa ctwrapper functions find_next library find_list Returns the next resource from the list of resources found during a previous call to find_resources Parameters e library the visa library wrapped by ctypes find_list Describes a find list This parameter must be created by find_resources Returns Returns a string identifying the location of a device Return type unicode Py2 or str Py3 pyvisa ctwrapper functions find_resources library session query Queries a VISA system to locate the resources associated with a specified interface Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session unused just to uniform signatures e query A regular expression followed by an optional logical expression Use for all Returns find_list return_counter instrument_description Return type ViFindList int unicode Py2 or str Py3 pyvisa ctwrapper functions flush library session mask Manually flushes the specified buffers associated with formatted I O operations and or serial communication Parameters 44 Chapter 3 More information PyVISA Documentation Release 1 5 e library the visa library wrapped
11. gt print rm lt ResourceManager path to visa so gt Note In some cases PyVISA is not able to find the library for you resulting in an OSError To fix it find the library path yourself and pass it to the ResourceManager constructor You can also specify it in a configuration file as discussed in Configuring PyVISA Once that you havea ResourceManager you can access any instrument Every instrument is represented in the source by an object instance In this case I have a GPIB instrument with instrument number 14 so I create the instance i e variable called my_instrument accordingly with GPIB 14 is the instrument s resource name Notice that eventhough you have requeste an instrument due to the resource name get_instrument has given you an instance of GpibInstrument class a subclass of the more generic instrument gt gt gt print my_instrument lt GpibInstrument GPIB 14 gt See section VISA resource names for a short explanation of that Then I send the message JDN to the device which is the standard GPIB message for what are you or in some cases what s on your display at the moment 2 2 2 Listing connected instruments The resource manager object allows you to list available resources 6 Chapter 2 User guide PyVISA Documentation Release 1 5 gt gt gt rm list_resources ASRL1 ASRL2 or the most comprehensive list_resources_info which
12. Chapter 3 More information PyVISA Documentation Release 1 5 pyvisa ctwrapper functions move_asynchronously library session source_space source_offset source_width des tination_space destination_offset destination_width length Moves a block of data asynchronously Parameters library the visa library wrapped by ctypes session Unique logical identifier to a session source_space Specifies the address space of the source source_offset Offset of the starting address or register from which to read source_width Specifies the data width of the source destination_space Specifies the address space of the destination destination_offset Offset of the starting address or register to which to write destination_width Specifies the data width of the destination length Number of elements to transfer where the data width of the elements to transfer is identical to the source data width Returns Job identifier of this asynchronous move operation pyvisa ctwrapper functions move_in 16 library session space offset length ex tended False Moves an 16 bit block of data from the specified address space and offset to local memory Parameters library the visa library wrapped by ctypes session Unique logical identifier to a session space Specifies the address space Constants SPACE offset Offset in bytes of the address or register from which to read
13. Data to write to bus 8 bits for out_8 16 bits for out_16 and 32 bits for out_32 Return values None parse_resource Parse a resource string to get the interface information Call interface_type interface_board_number parse_resource session resource_name VISA name viParseRsrc Parameters session integer Resource Manager session should always be the Default Resource Manager for VISA returned from open_default_resource_manager resource_name string Unique symbolic name of a resource Return values interface_type integer Interface type of the given resource string interface_board_number integer Board number of the interface of the given resource string 4 3 Legacy API 81 PyVISA Documentation Release 1 5 parse_resource_extended Parse a resource string to get extended interface information Attention Calling this function may raise an Att ributeError because some older VISA implementation don t have the function viParseRsrcEx Call interface_type interface_board_number resource_class unaliased_expanded_resource_name alias_if_exists parse_resource_extended session resource_name VISA name viParseRsrcEx Parameters session integer Resource Manager session should always be the Default Resource Manager for VISA returned from open_default_resource_manager resource_name string Unique symbolic name of a resource Return values interface_type integer Interface type of the g
14. Discard event occurrences for specified event types and mechanisms in a session Call discard_events vi event_type mechanism VISA name viDiscardEvents Parameters vi integer Unique logical identifier to a session event_type integer Logical event identifier mechanism integer Specifies the mechanisms for which the events are to be discarded The VI_QUEUE value is specified for the queuing mechanism and the VI_SUSPEND_HNDLR value is specified for the pending events in the callback mechanism It is possible to specify both mechanisms simultaneously by specifying VI_ALL_MECH Return values None enable_event Enable notification of a specified event Call enable_event vi event_type mechanism context VISA name viEnableEvent Parameters vi integer Unique logical identifier to a session event_type integer Logical event identifier mechanism integer Specifies event handling mechanisms to be enabled The queuing mechanism is enabled by specifying VI_QUEUE and the callback mechanism is enabled by specifying VI_HNDLR or VI_SUSPEND_HNDLR It is possible to enable both mechanisms simultane ously by specifying bit wise or of VI_QUEUE and one of the two mode values for the call back mechanism 72 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 context integer optional According to the VISA specification this must be Vi_NULL always This is also the default valu
15. QUEUE Handler SUSPEND_HNDLR ALL_MECH enable_event library session event_type mechanism context 0 Enable event occurrences for specified event types and mechanisms in a session Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e event_type Logical event identifier e mechanism Specifies event handling mechanisms to be disabled Constants QUEUE Handler SUSPEND_HNDLR e context find_next library find_list Returns the next resource from the list of resources found during a previous call to find_resources Parameters e library the visa library wrapped by ctypes e find_list Describes a find list This parameter must be created by find_resources Returns Returns a string identifying the location of a device Return type unicode Py2 or str Py3 find_resources library session query Queries a VISA system to locate the resources associated with a specified interface Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session unused just to uniform signatures e query A regular expression followed by an optional logical expression Use for all Returns find_list return_counter instrument_description Return type ViFindList int unicode Py2 or str Py3 flush library session mask Manually flushes the specified buffers associated with formatted I O
16. a string from the device Reading stops when the device stops sending e g by setting appropriate bus lines or the termination characters sequence was detected Attention Only the last character of the termination characters is really used to stop reading however the whole sequence is compared to the ending of the read string message If they don t match a warning is issued All line ending characters are stripped from the end of the string Return type str read_raw size None Read the unmodified string sent from the instrument to the computer In contrast to read no termination characters are stripped Return type bytes read_termination Read termination character read_values fmt None Read a list of floating point values from the device Parameters fmt the format of the values If given it overrides the class attribute val ues_format Possible values are bitwise disjunctions of the above constants ascii single double and big_endian Default is ascii Returns the list of read values Return type list send_end Whether or not to assert EOI or something equivalent after each write operation term_chars Set or read a new termination character sequence property Normally you just give the new termination sequence which is appended to each write operation unless it s already there and expected as the ending mark during each read operation A typical example is CR LF or just CR If you assign
17. bus poke_8 library session address data Write an 8 bit value from the specified address Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e address Source address to read the value e data value to be written to the bus Returns Data read from bus read library session count Reads data from device or interface synchronously Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e count Number of bytes to be read Returns data read Return type bytes read _asynchronously library session count Reads data from device or interface asynchronously Parameters library the visa library wrapped by ctypes e session Unique logical identifier to a session e count Number of bytes to be read 34 Chapter 3 More information PyVISA Documentation Release 1 5 Returns ctypes buffer with result jobid read_stb library session Reads a status byte of the service request Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session Returns Service request status byte read_to_file library session filename count Read data synchronously and store the transferred data in a file Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session
18. by ctypes e session Unique logical identifier to a session e mask Specifies the action to be taken with flushing the buffer Constants READ WRITE IO pyvisa ctwrapper functions get_attribute library session attribute Retrieves the state of an attribute Parameters e library the visa library wrapped by ctypes session Unique logical identifier to a session event or find list attribute Resource attribute for which the state query is made see Attributes Returns The state of the queried attribute for a specified resource Return type unicode Py2 or str Py3 list or other type pyvisa ctwrapper functions get_default_resource_ manager library A deprecated alias See VPP 4 3 rule 4 3 5 and observation 4 3 2 pyvisa ctwrapper functions gpib_command library session data Write GPIB command bytes on the bus Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e data bytes data tor write Returns Number of written bytes pyvisa ctwrapper functions gpib_control_atn library session mode Specifies the state of the ATN line and the local active controller state Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e mode Specifies the state of the ATN line and optionally the local active controller state Constants GPIB_ATN pyvisa ctwrapper fu
19. count VISA name viReadAsync Parameters vi integer Unique logical identifier to a session count integer Maximal number of bytes to be read Return values buffer ctypes string buffer Represents the buffer with the data received from device It s not a native Python data type because it s filled in the background i e asynchronously After you assured that the reading is finished you get its value with buffer raw return_count You get return_count via the attribute VI_ATTR_RET_COUNT See the VISA reference for further information job_id ViJobld Represents the location of a variable that will be set to the job identifier of this asynchronous read operation 84 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 read_stb Read a status byte of the service request Call status read_stb vi VISA name viReadSTB Parameters vi integer Unique logical identifier to a session Return values status integer Service request status byte read_to file Read data synchronously and store the transferred data in a file Call return_count read_to_file vi filename count VISA name viReadToFile Parameters vi integer Unique logical identifier to a session file_name string Name of file to which data will be written count integer Maximal number of bytes to be read Return values return_count integer Number of bytes actually transferred scanf Read convert and format data using
20. ctypes session Unique logical identifier to a session request_type_bitmap_field bmRequestType parameter of the setup stage of a USB con trol transfer request_id bRequest parameter of the setup stage of a USB control transfer request_value wValue parameter of the setup stage of a USB control transfer index wIndex parameter of the setup stage of a USB control transfer This is usually the index of the interface or endpoint data The data buffer that sends the data in the optional data stage of the control transfer vxi_command_query library session mode command Sends the device a miscellaneous command or query and or retrieves the response to a previous query Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e mode Specifies whether to issue a command and or retrieve a response Con stants VXI_CMD VXI_RESP e command The miscellaneous command to send Returns The response retrieved from the device wait_on_event library session in_event_type timeout Waits for an occurrence of the specified event for a given session Parameters e library the visa library wrapped by ctypes 3 4 API 37 PyVISA Documentation Release 1 5 e session Unique logical identifier to a session e in_event_type Logical identifier of the event s to wait for e timeout Absolute time period in time units that
21. e library the visa library wrapped by ctypes e session Unique logical identifier to a session source_space Specifies the address space of the source e source_offset Offset of the starting address or register from which to read e source_width Specifies the data width of the source 3 4 API 29 PyVISA Documentation Release 1 5 e destination_space Specifies the address space of the destination e destination_offset Offset of the starting address or register to which to write e destination_width Specifies the data width of the destination e length Number of elements to transfer where the data width of the elements to transfer 1s identical to the source data width Returns Job identifier of this asynchronous move operation move_in_16 library session space offset length extended False Moves an 16 bit block of data from the specified address space and offset to local memory Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e space Specifies the address space Constants SPACE e offset Offset in bytes of the address or register from which to read e length Number of elements to transfer where the data width of the elements to transfer is identical to the source data width e extended Use 64 bits offset independent of the platform Returns Data read from bus Corresponds to viMoveln16 functions
22. filename Name of file to which data will be written e count Number of bytes to be read Returns Number of bytes actually transferred resource_manager Default resource manager object for this library set_attribute library session attribute attribute_state Sets the state of an attribute Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session attribute Attribute for which the state is to be modified Attributes e attribute_state The state of the attribute to be set for the specified object set_buffer library session mask size Sets the size for the formatted I O and or low level I O communication buffer s Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e mask Specifies the type of buffer Constants READ BUF WRITE_BUF O_IN_BUF IO_OUT_BUF e size The size to be set for the specified buffer s status Last return value of the library status_description library session status Returns a user readable description of the status code passed to the operation Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session 3 4 API 35 PyVISA Documentation Release 1 5 e status Status code to interpret Returns The user readable string interpretation of the status code passed to the operati
23. identifier to a session param space Specifies the address space Constants SPACE param offset Offset in bytes of the address or register from which to read param data Data to write to bus param extended Use 64 bits offset independent of the platform Corresponds to viOut8 functions of the visa library parse_resource library session resource_name Parse a resource string to get the interface information Parameters e library the visa library wrapped by ctypes 32 Chapter 3 More information PyVISA Documentation Release 1 5 e session Resource Manager session should always be the Default Resource Manager for VISA returned from open_default_resource_manager e resource_name Unique symbolic name of a resource Returns Resource information with interface type and board number Return type class ResourceInfo parse_resource_extended library session resource_name Parse a resource string to get extended interface information Parameters e library the visa library wrapped by ctypes e session Resource Manager session should always be the Default Resource Manager for VISA returned from open_default_resource_manager e resource_name Unique symbolic name of a resource Returns Resource information Return type class ResourceInfo peek_16 library session address Read an 16 bit value from the specified address Parameters e library the visa library wrapped by
24. last_bit_end_input read will terminate as soon as a character arrives with its last data bit set term_chars_end_input read will terminate as soon as the last character of term_chars is received The default value is term_chars_end_input 66 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 4 3 3 Common properties of instrument variables 4 3 4 Timeouts Very most VISA I O operations may be performed with a timeout If a timeout is set every operation that takes longer than the timeout is aborted and an exception is raised Timeouts are given per instrument For all PyVISA objects a timeout is set with my_device timeout 25 Here my_device may be a device an interface or whatever and its timeout is set to 23 seconds Floating point values are allowed If you set it to zero all operations must succeed instantaneously You must not set it to None Instead if you want to remove the timeout just say del my_device timeout Now every operation of the resource takes as long as it takes even indefinitely if necessary The default timeout is 5 seconds but you can change it when creating the device object my_instrument instrument ASRL1 timeout 8 This creates the object variable my_instrument and sets its timeout to 8 seconds In this context a timeout value of None is allowed which removes the timeout for this device Note that your local VISA library may round up this value heavily I exper
25. length Number of elements to transfer where the data width of the elements to transfer is identical to the source data width extended Use 64 bits offset independent of the platform Returns Data read from bus Corresponds to viMoveln16 functions of the visa library pyvisa ctwrapper functions move_in_32 library session space offset length ex tended False Moves an 32 bit block of data from the specified address space and offset to local memory Parameters library the visa library wrapped by ctypes session Unique logical identifier to a session space Specifies the address space Constants SPACE offset Offset in bytes of the address or register from which to read length Number of elements to transfer where the data width of the elements to transfer is identical to the source data width 3 4 API 49 PyVISA Documentation Release 1 5 e extended Use 64 bits offset independent of the platform Returns Data read from bus Corresponds to viMoveln32 functions of the visa library pyvisa ctwrapper functions move_in_8 library session space offset length extended False Moves an 8 bit block of data from the specified address space and offset to local memory Parameters library the visa library wrapped by ctypes session Unique logical identifier to a session space Specifies the address space Constants SPACE offset Offset in bytes of
26. of the platform Returns Returns the offset of the allocated memory memory_free library session offset extended False Frees memory previously allocated using the memory_allocation operation Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session offset Offset of the memory to free e extended Use 64 bits offset independent of the platform move library session Source_space source_offset source_width destination_space destination_offset destination_width length Moves a block of data Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e source_space Specifies the address space of the source e source_offset Offset of the starting address or register from which to read e source_width Specifies the data width of the source e destination_space Specifies the address space of the destination e destination_offset Offset of the starting address or register to which to write destination_width Specifies the data width of the destination e length Number of elements to transfer where the data width of the elements to transfer is identical to the source data width move_asynchronously library session source_space source_offset source_width destina tion_space destination_offset destination_width length Moves a block of data asynchronously Parameters
27. or in 64 bits by running arch x86_64 python myscript py You can create an alias by adding the following line alias python32 arch 1386 python into your bashrc or profile or bash_profile or whatever file depending on which shell you are using You can also create a virtual environment for this 3 3 7 Where can get more information about VISA e The original VISA docs VISA specification scroll down to the end VISA library specification VISA specification for textual languages e The very good VISA manuals from National Instruments s VISA NI VISA User Manual 22 Chapter 3 More information PyVISA Documentation Release 1 5 NI VISA Programmer Reference Manual NI VISA help file in HTML 3 4 API 3 4 1 Highlevel module class pyvisa highlevel VisaLibrary High level VISA Library wrapper The easiest way to instantiate the library is to let pyvisa find the right one for you This looks first in your configuration file pyvisarc If it fails it uses ctypes util find_library to try to locate a library in a way similar to what the compiler does gt gt gt visa_library VisaLibrary But you can also specify the path gt gt gt visa_library VisaLibrary my path visa so Or use the from_paths constructor if you want to try multiple paths gt gt gt visa_library VisaLibrary from_paths my path visa so maybe this visa so Par
28. sensors and the like This document covers the easy to use visa module of the PyVISA package It implements control of measurement devices in a straightforward and convenient way The design goal is to combine HTBasic s simplicity with Python s modern syntax and powerful set of libraries Py VISA doesn t implement VISA itself Instead PyVISA provides bindings to the VISA library a DLL or shared object file This library is usually shipped with your GPIB interface or software like LabVIEW Alternatively you can download it from your favourite equipment vendor National Instruments Agilent etc It can be downloaded at the PyVISA project page You can report bugs there too Additionally P m happy about feedback from people who ve given it a try So far we have positive reports of various National Instruments GPIB adapters connected through PCI USB and RS232 the Agilent 82357A and SRS lock in amplifiers for both Windows and Linux However Id be really surprised about negative reports anyway due to the high abstraction level of PyVISA As far as USB instruments are concerned you must make sure that they act as ordinary USB devices and not as so called HDI devices like keyboard and mouse Contents e About the legacy visa module Anexample Example for serial RS232 device A more complex example VISA resource names 4 1 1 An example Let s go in medias res and have a look at a simple exam
29. separately that the device actually sends in this format In some cases it may be necessary to set the byte order also known as endianness PyVISA assumes little endian as default Some instruments call this swapped byte order However there is also big endian byte order In this case you have to append big_endian to your values format my_instrument instrument GPIB 12 values_format single big_endian Example In order to demonstrate how easy reading binary data can be remember our example from section A more complex example You just have to append the lines keithley write format data sreal keithley values_format single to the initialisation commands and all measurement data will be transmitted as binary You will only notice the increased speed as PyVISA converts it into the same list of values as before 2 5 3 Termination characters Somehow the computer must detect when the device is finished with sending a message It does so by using different methods depending on the bus system In most cases you don t need to worry about termination characters because the defaults are very good However 1f you have trouble you may influence termination characters with PyVISA Termination characters may be one character or a sequence of characters Whenever this character or sequence occurs in the input stream the read operation is terminated and the read message is given to the calling application The next read opera
30. session to the Default Resource Manager resource Parameters library the visa library wrapped by ctypes Returns Unique logical identifier to a Default Resource Manager session out_16 library session space offset data extended False Write in an 16 bit value from the specified memory space and offset param library the visa library wrapped by ctypes param session Unique logical identifier to a session param space Specifies the address space Constants SPACE param offset Offset in bytes of the address or register from which to read param data Data to write to bus param extended Use 64 bits offset independent of the platform Corresponds to viOut16 functions of the visa library out_32 library session space offset data extended False Write in an 32 bit value from the specified memory space and offset param library the visa library wrapped by ctypes param session Unique logical identifier to a session param space Specifies the address space Constants SPACE param offset Offset in bytes of the address or register from which to read param data Data to write to bus param extended Use 64 bits offset independent of the platform Corresponds to viOut32 functions of the visa library out_8 library session space offset data extended False Write in an 8 bit value from the specified memory space and offset param library the visa library wrapped by ctypes param session Unique logical
31. space offset length buffer_8 move_out_16 vi space offset length buffer_16 move_out_32 vi space offset length buffer_32 VISA name viMoveOut8 viMoveOut16 viMoveOut32 Parameters vi integer Unique logical identifier to a session space integer Specifies the address space offset ViBusAddress Offset in bytes of the starting address or register from which to write length integer Number of elements to transfer where the data width of the elements to transfer is identical to data width 8 16 or 32 bits buffer_8 buffer_16 buffer_32 sequence of integers Data to write to bus This may be a list or a tuple however in any case in must contain integers Return values None open Open a session to the specified device Call vi open session resource_name access_mode open_timeout VISA name viOpen Parameters session integer Resource Manager session should always be the Default Resource Manager for VISA returned from open_default_resource_manager resource_name string Unique symbolic name of a resource access_mode integer optional Defaults to VI_NO_LOCK Specifies the modes by which the re source is to be accessed The value VI_EXCLUSIVE_LOCK is used to acquire an exclusive lock immediately upon opening a session if a lock cannot be acquired the session is closed and an error is returned The value VI_LOAD_ CONF IG is used to configure attributes to values specified by some external configuration
32. sprintf or sscanf of vpp43 rewrite as pure python code see below If you were using Instrument delay change your code or use Instrument ask_delay see below 3 1 2 A more detailed description Dropped support for string related functions The VISA library includes functions to search and manipulate strings such as printf queryf scanf sprintf and sscanf This makes sense as visa involves a lot of string handling operations The original Py VISA implementation wrapped these functions But these operations are easily expressed in pure python and therefore were rarely used PyVISA 1 5 keeps these functions for backwards compatibility but it will be removed in 1 6 We suggest that you replace such functions by a pure python version Isolated low level wrapping module In the original PyVISA implementation the low level implementation vpp43 was mixed with higher level constructs such as VisaLibrary VisaException and error messages The VISA library was wrapped using ctypes In 1 5 we refactored it as ctwrapper also a ctypes wrapper module but it only depends on the constants definitions constants py This allows us to test the foreign function calls by isolating them from higher level abstractions More importantly it also allows us to build new low level modules that can be used as drop in replacements for ctwrapper in high level modules We have two modules planned e a Mock module that allows you to test a Py VISA program even
33. the address or register from which to read length Number of elements to transfer where the data width of the elements to transfer is identical to the source data width extended Use 64 bits offset independent of the platform Returns Data read from bus Corresponds to viMoveln8 functions of the visa library pyvisa ctwrapper functions move_out_16 library session space offset length data ex tended False Moves an 16 bit block of data from local memory to the specified address space and offset Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session space Specifies the address space Constants SPACE offset Offset in bytes of the address or register from which to read length Number of elements to transfer where the data width of the elements to transfer is identical to the source data width data Data to write to bus extended Use 64 bits offset independent of the platform Corresponds to viMoveOut16 functions of the visa library pyvisa ctwrapper functions move_out_32 library session space offset length data ex tended False Moves an 32 bit block of data from local memory to the specified address space and offset Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session space Specifies the address space Constants SPACE offset Offset i
34. the instrument you want to connect to Generally it starts with the bus type followed by a double colon followed by the number within the bus For example GPIB 10 denotes the GPIB instrument with the number 10 If you have two GPIB boards and the instrument is connected to board number 1 you must write GPIB1 10 4 1 About the legacy visa module 61 PyVISA Documentation Release 1 5 As for the bus things like GPIB USB ASRL for serial parallel interface are possible So for connecting to an instrument at COM2 the resource name is ASRL2 Since only one instrument can be connected with one serial interface there is no double colon parameter However most VISA systems allow aliases such as COM2 or LPTI You may also add your own aliases The resource name is case insensitive It doesn t matter whether you say ASRL2 or asrl2 For further information I have to refer you to a comprehensive VISA description like http www ni com pdf manuals 370423a pdf Note This is a legacy module kept for backwards compatiblity with PyVISA lt 1 5 and will be deprecated in future versions of PyVISA You are strongly encouraged to switch to the new implementation 4 2 About the legacy vpp43 module This module vpp4 3 is a cautious yet thorough adaption of the VISA specification for Python The textual languages VISA specification can t be implemented as is because P
35. the resource shall wait for a specified event to occur before returning the time elapsed error The time unit is in milliseconds Returns Logical identifier of the event actually received A handle specifying the unique occur rence of an event write library session data Writes data to device or interface synchronously Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e data str data to be written Returns Number of bytes actually transferred write asynchronously library session data Writes data to device or interface asynchronously Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e data data to be written Returns Job ID of this asynchronous write operation write _from_file library session filename count Take data from a file and write it out synchronously Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e filename Name of file from which data will be read e count Number of bytes to be written Returns Number of bytes actually transferred class pyvisa highlevel ResourceManager VISA Resource Manager Parameters visa_library VisaLibrary Instance or path of the VISA library if not given the de fault for the platform will be used get_instrument resource_name kwargs Return an i
36. they may be limited to certain interface devices such as the vendor s GPIB card The VISA specification has explicit bindings to Visual Basic C and G LabVIEW s graphical language However you can use VISA with any language capable of calling functions in a shared library dll so dylib PyVISA is Python wrapper for such shared library PyVISA Documentation Release 1 5 4 Chapter 1 General overview CHAPTER 2 User guide 2 1 Installation PyVISA is a wrapper around the National Instruments s VISA library which you need to download and install in order to use PyVISA getting_nivisa PyVISA has no additional dependencies except Python itself In runs on Python 2 6 and 3 2 Warning PyVISA works with 32 and 64 bit Python and can deal with 32 and 64 bit VISA libraries without any extra configuration What PyVISA cannot do is open a 32 bit VISA library while running in 64 bit Python or the other way around You need to make sure that the Python and VISA library have the same bitness You can install it using pip pip install pyvisa or using easy_ install easy_install pyvisa That s all You can check that PyVISA is correctly installed by starting up python and importing PyVISA gt gt gt import visa gt gt gt lib visa VisaLibrary If you encounter any problem take a look at the Frequently asked questions 2 1 1 Getting the code You can also get the code from PyPI or
37. they refer to different foreign libraries In code this means gt gt gt libl visa VisaLibrary path to my libvisa so 7 gt gt gt 1ib2 visa VisaLibrary path to my libvisa so 7 gt gt gt lib3 visa VisaLibrary path to my libvisa so 8 gt gt gt libl is lib2 True gt gt gt libl is 11b3 False Most of the time you will not need access to a VisaLibrary object but to a ResourceManager You can do gt gt gt lib visa VisaLibrary path to my libvisa so 7 gt gt gt rm lib resource_manager or equivalently gt gt gt rm visa ResourceManager path to my libvisa so 7 Note If the path for the library is not given the path is obtained from the user settings file if exists or guessed from the OS You can still access the legacy classes and global objects gt gt gt from pyvisa legacy import vpp43 gt gt gt from pyvisa legacy import visa_library resource_manager In 1 5 visa_library and resource_manager instances of the legacy classes will be instantiated on import VisaLibrary methods as way to call Visa functions In the original PyVISA implementation the VisaLibrary class was just having a reference to the ctypes library and a few functions In 1 5 we introduced a new VisaLibrary class pyvisa highlevel which has every single low level function defined in ctwrapper as bound methods In code this means that you can do 3 1 Migrating from PyVISA lt
38. time 500ms and the number of readings 10 to the instrument I won t explain it in detail Have a look at an SCPI and or Keithley 2000 manual gt gt gt interval_in_ms 500 gt gt gt number_of_readings 10 gt gt gt keithley write status measurement enable 512 xsre 1 gt gt gt keithley write sample count d number_of_readings gt gt gt keithley write trigger source bus gt gt gt keithley write trigger delay 3f interval_in_ms 1000 0 gt gt gt keithley write trace points d number_of_readings gt gt gt keithley write trace feed sensel feed control next Okay now the instrument is prepared to do the measurement The next three lines make the instrument waiting for a trigger pulse trigger it and wait until it sends a service request gt gt gt keithley write initiate gt gt gt keithley trigger gt gt gt keithley wait_for_srq 2 2 Tutorial 7 PyVISA Documentation Release 1 5 With sending the service request the instrument tells us that the measurement has been finished and that the results are ready for transmission We could read them with keithley ask trace data however then we d get NDCV 000 0004E 0 NDCV 000 0005E 0 NDCV 000 0004E 0 NDCV 000 0007E 0 NDCV 000 0000E 0 NDCV 000 0007E 0 NDCV 000 0008E 0 NDCV 000 0004E 0 NDCV 000 0002E 0 NDCV 000 0005E 0 which we would have to convert to a Pyth
39. utility 1f this value is not used the session uses the de fault values provided by this specification Multiple access modes can be used simultaneously by specifying a bitwise OR of the above values open_timeout integer optional If the access_mode parameter requests a lock then this param eter specifies the absolute time period in milliseconds that the resource waits to get un locked before this operation returns an error otherwise this parameter is ignored Defaults to VI_TMO_ IMMEDIATE Return values vi integer Unique logical identifier reference to a session 80 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 open_default_resource_manager Return a session to the Default Resource Manager resource Call session open_default_resource_manager VISA name viOpenDefaultRM Parameters None Return values session integer Unique logical identifier to a Default Resource Manager session get_default_resource_manager This is a deprecated alias for open_default_resource_manager out_8 out_16 out_32 Call out_8 vi space offset value_8 out_16 vi space offset value_16 out_32 vi space offset value_32 VISA name viOut8 viOutl6 viOut32 Parameters vi integer Unique logical identifier to a session space integer Specifies the address space offset integer Offset in bytes of the address or register to which to write value_8 value_16 value_32 integer
40. values with single precision i e four bytes each double The same as single but with values of double precision eight bytes each 4 3 Legacy API 67 PyVISA Documentation Release 1 5 You can set the form of transfer with the property values_format either with the generation of the object my_instrument instrument GPIB 12 values_format single or later by setting the property directly my_instrument values_format single Setting this option affects the methods read_values and ask_for_values In particular you must assure separately that the device actually sends in this format In some cases it may be necessary to set the byte order also known as endianness PyVISA assumes little endian as default Some instruments call this swapped byte order However there is also big endian byte order In this case you have to append big_endian to your values format my_instrument instrument GPIB 12 values_format single big_endian Example In order to demonstrate how easy reading binary data can be remember our example from section A more complex example You just have to append the lines keithley write format data sreal keithley values_format single to the initialisation commands and all measurement data will be transmitted as binary You will only notice the increased speed as PyVISA converts it into the same list of values as before 4 3 7 Termination characters Somehow the comput
41. 1 5 19 PyVISA Documentation Release 1 5 gt gt gt import visa gt gt gt lib visa VisaLibrary path to my libvisa so 7 gt gt gt print lib read_stb session It also has every single VISA foreign function in the underlying library as static method In code this means that you can do gt gt gt lib visa VisaLibrary path to my libvisa so 7 gt gt gt status ctypes c_ushort gt gt gt ret library viReadSTB session ctypes byref status gt gt gt print ret value Removal of Instrument delay and added Instrument ask_delay In the original Py VISA implementation Instrument takes a delay argument that adds a pause after each write operation This also can be changed using the delay attribute In PyVISA 1 5 delay is removed Delays after write operations must be added to the application code Instead a new attribute and argument ask_delay is available This allows you to pause between write and read operations inside ask Additionally ask takes an optional argument called delay allowing you to change it for each method call Deprecated term_chars and automatic removal of CR LF In the original PyVISA implementation Instrument takes a term_chars argument to change at the read and write termination characters If this argument is None CR LF is appended to each outgoing message and not expected for incoming messages although removed if present In PyVISA 1 5 term_chars is replaced by read
42. 32 USB with Python programs As an example reading self identification from a Keithley Multimeter with GPIB number 12 is as easy as three lines of Python code gt gt gt import visa gt gt gt rm visa ResourceManager gt gt gt rm list_resources ASRL1 ASRL2 GPIB 12 gt gt gt keithley rm get_instrument GPIB 12 gt gt gt print keithley ask x IDN That s the whole program really It works on Windows Linux and Mac with arbitrary adapters e g National Instruments Agilent Tektronix Stanford Research Systems In order to achieve this PyVISA relies on an external library file which is bundled with hardware and software of those vendors Contents 1 PyVISA Documentation Release 1 5 2 Contents CHAPTER 1 General overview The programming of measurement instruments can be real pain There are many different protocols sent over many different interfaces and bus systems GPIB RS232 USB For every programming language you want to use you have to find libraries that support both your device and its bus system In order to ease this unfortunate situation the VISA Virtual Instrument Software Architecture specification was defined in the middle of the 90ies Today VISA is implemented on all significant operating systems A couple of vendors offer VISA libraries partly with free download These libraries work together with arbitrary peripherical devices although
43. A Documentation Release 1 5 out_event_type integer Logical identifier of the event actually received out_context ViEvent A handle specifying the unique occurrence of an event write Write data to device synchronously Call return_count write vi buffer VISA name viWrite Parameters vi integer Unique logical identifier to a session buffer string Contains the data block to be sent to the device Return values return_count integer The number of bytes actually transferred write_asynchronously Write data to device asynchronously Call job_id write_asynchronously vi buffer VISA name viWriteAsync Parameters vi integer Unique logical identifier to a session buffer string Contains the data block to be sent to the device Return values job_id ViJobld The job identifier of this asynchronous write operation write_from_file Take data from a file and write it out synchronously Call return_count write_from_file vi filename count VISA name viWriteFromFile Parameters vi integer Unique logical identifier to a session filename string Name of file from which data will be read count integer Maximal number of bytes to be written Return values return_count integer Number of bytes actually transferred 4 3 Legacy API 91 PyVISA Documentation Release 1 5 92 Chapter 4 Legacy Modules Python Module Index p pyvisa ctwrapper functions 42 93
44. ControlREN Parameters 74 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 vi integer Unique logical identifier to a session mode integer Specifies the state of the REN line and optionally the device remote local state See the Description section for actual values Return values None gpib_pass_control Tell the GPIB device at the specified address to become controller in charge CIC Call gpib_pass_control vi primary_address secondary_address VISA name viGpibPassControl Parameters vi integer Unique logical identifier to a session primary_address integer Primary address of the GPIB device to which you want to pass control secondary_address integer Secondary address of the targeted GPIB device If the tar geted device does not have a secondary address this parameter should contain the value VI_NO_SEC_ADDR Return values None gpib_send_ifc Pulse the interface clear line IFC for at least 100 microseconds Call gpib_send_ifc vi VISA name viGpibSendIFC Parameters vi integer Unique logical identifier to a session Return values None in_8 in_16 in_32 Read in an 8 bit 16 bit or 32 bit value from the specified memory space and offset Call value_8 in_8 vi space offset value_16 in_16 vi space offset value_32 in_32 vi space offset VISA name viln8 viln16 viln32 Parameters vi integer Unique logical identifier to a session space integer Specifies the
45. GitHub You can either clone the public repository git clone git github com hgrecco pyvisa git Download the tarball curl OL https github com hgrecco pyvisa tarball master Or download the zipball curl OL https github com hgrecco pyvisa zipball master PyVISA Documentation Release 1 5 Once you have a copy of the source you can embed it in your Python package or install it into your site packages easily python setup py install Note If you have an old system installation of Python and you don t want to mess with it you can try Anaconda CE It is a free Python distribution by Continuum Analytics that includes many scientific packages 2 2 Tutorial Note If you have been using PyVISA before version 1 5 you might want to read Migrating from PyVISA lt 1 5 2 2 1 An example Let s go in medias res and have a look at a simple example gt gt gt import visa gt gt gt rm visa ResourceManager gt gt gt my_instrument rm get_instrument GPIB 14 gt gt gt my_instrument write IDN gt gt gt print my_instrument read This example already shows the two main design goals of PyVISA preferring simplicity over generality and doing it the object oriented way Afer importing visa we create a ResourceManager object If called without arguments PyVISA will try to find the VISA shared for you You can check the location of the shared library used simply by gt gt
46. PyVISA Documentation Release 1 5 PyVISA Authors August 23 2014 Contents 1 General overview 3 2 User guide 5 21 Installation 3 4 ori a A E a e it amp 5 22 CNOA ss a a RA a ae eed Boke E Aa ee ae E aas i aR a E do Boe 6 2 3 Configure PYVISA oe siue ci PA Oe ade e wa a ed at 8 24 Advanced s s sacs mid a Gok hw e i a eK A RS See amp e SO Bd bee amp 9 2 9 Instruments 2 566 ew a SHADER RAMEE we ee Rae eRe E 10 26 ATEOHECIULS sesa eh pS A Geet hee He Shee hd BA AY YO haw Hees 15 3 More information 17 3 1 Migrating from PYVISA lt 1 5 uu E a o 17 3 2 Contributingito PyVISA xo siria ra a e A AA 20 3 3 Frequently asked QUESIONS voii e a de a RA BA 21 3A A E bea Me dee eee bea es 23 4 Legacy Modules 59 Al Aboutthelesacy visa module 2 245422 44 Ges We ee dew See ee Se ee owe eS 59 4 2 Aboutthe legacy vpp43 module s r ste spider be ee Ge ee ee be be Soe amp A 62 4y LesacyAPh ig 24 64g hh RE RR RE BS Ba ak eA EON ee LSS ee Ee 63 Python Module Index 93 PyVISA Documentation Release 1 5 PyVISA Warning This documentation corresponds to PyVISA 1 5 which is currently under development You can install it from the GitHub using the following command pip install U https github com hgrecco pyvisa zipball master The old documentations is here http pyvisa readthedocs org en 1 4 The PyVISA package enables you to control all kinds of measurement equipment through various busses GPIB RS2
47. Sets the size for the formatted I O and or low level I O communication buffer s Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session 54 Chapter 3 More information PyVISA Documentation Release 1 5 e mask Specifies the type of buffer Constants READ_BUF WRITE_BUF IO_IN_BUF IO_OUT_BUF e size The size to be set for the specified buffer s pyvisa ctwrapper functions status_description library session status Returns a user readable description of the status code passed to the operation Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e status Status code to interpret Returns The user readable string interpretation of the status code passed to the operation Return type unicode Py2 or str Py3 pyvisa ctwrapper functions terminate library session degree job_id Requests a VISA session to terminate normal execution of an operation Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e degree Constants NULL e job_id Specifies an operation identifier pyvisa ctwrapper functions uninstall_handler library session event_type handler user_handle None Uninstalls handlers for events Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a
48. The resource name is case insensitive It doesn t matter whether you say ASRL2 or asrl2 For further information I have to refer you to a comprehensive VISA description like http www ni com pdf manuals 370423a pdf 2 3 Configuring PyVISA In most cases PyVISA will be able to find the location of the shared visa library If this does not work or you want to use another one you need to provide the library path to the VisaLibrary or ResourceManager constructor gt gt gt visalib VisaLibrary path to library or gt gt gt rm ResourceManager Path to library 8 Chapter 2 User guide PyVISA Documentation Release 1 5 You can make this library the default for all PyVISA applications by using a configuration file called pyvisarc mind the leading dot in your home directory Operating System Location Windows NT lt root gt WINNT Profiles lt username gt Windows 2000 XP and 2003 lt root gt Documents and Settings lt username gt Windows Vista 7 or 8 lt root gt Users lt username gt Mac OS X Users lt username gt Linux home lt username gt depends on the distro For example in Windows XP place it in your user folder Documents and Settings folder e g C Documents and Settings smith pyvisarc if smith is the name of your login account This file has the format of an INI file For example if the library is at usr lib libvisa so 7 the file py
49. _manager e resource_name Unique symbolic name of a resource e access_mode Specifies the mode by which the resource is to be accessed Con stants NULL or Constants LOCK e open_timeout Specifies the maximum time period in milliseconds that this operation waits before returning an error Returns Unique logical identifier reference to a session pyvisa ctwrapper functions open_default_resource_manager library This function returns a session to the Default Resource Manager resource Parameters library the visa library wrapped by ctypes Returns Unique logical identifier to a Default Resource Manager session pyvisa ctwrapper functions out_16 library session space offset data extended False Write in an 16 bit value from the specified memory space and offset param library the visa library wrapped by ctypes param session Unique logical identifier to a session param space Specifies the address space Constants SPACE param offset Offset in bytes of the address or register from which to read param data Data to write to bus param extended Use 64 bits offset independent of the platform Corresponds to viOut16 functions of the visa library pyvisa ctwrapper functions out_32 library session space offset data extended False Write in an 32 bit value from the specified memory space and offset param library the visa library wrapped by ctypes param session Unique logical identifier t
50. _termination and write_termination In this way you can set indepen dently the termination for each operation term_chars is still present in 1 5 but will be removed and sets both at the same time Automatic removal of CR LF is still present in 1 5 but will be removed in 1 6 3 2 Contributing to PyVISA You can contribute in different ways 3 2 1 Report issues You can report any issues with the package the documentation to the PyVISA issue tracker Also feel free to submit feature requests comments or questions In some cases platform specific information is required If you think this is the case run the following command and paste the output into the issue python c from pyvisa import util util get_debug_info 3 2 2 Contribute code To contribute fixes code or documentation to PyVISA send us a patch or fork PyVISA in github and submit the changes using a pull request 20 Chapter 3 More information PyVISA Documentation Release 1 5 3 3 Frequently asked questions 3 3 1 Is PyVISA endorsed by National Instruments No PyVISA is developed independently of National Instrument as a wrapper for the VISA library 3 3 2 Who makes PyVISA PyVISA was originally programmed by Torsten Bronger and Gregor Thalhammer It is based on earlier experiences by Thalhammer It was maintained from March 2012 to August 2013 by Florian Bauer It is currently maintained by Hernan E Grecco lt hernan grecco O gmail com gt Ta
51. address integer Specifies the destination address to store the value value_8 value_16 value_32 integer Data to write to bus 8 bits for poke_8 16 bits for poke_16 and 32 bits for poke_32 Return values None printf Convert format and send the parameters to the device as specified by the format string Warning The current implementation only supports the following C data types Long double and char strings Thus you can only use these three data types in format strings for printf scanf and the like Call printf vi write_format VISA name viPrintf Parameters vi integer Unique logical identifier to a session write_format string String describing the format for arguments integers floats or strings Arguments sent to the device according to write_format Return values None queryf Perform a formatted write and read through a single operation invocation Warning The current implementation only supports the following C data types Long double and char strings Thus you can only use these three data types in format strings for printf scanf and the like Call value1 value2 queryf vi write_format read_format maximal_string_length 1024 VISA name viQueryf Parameters vi integer Unique logical identifier to a session write_format string String describing the format for arguments read_format string String describing the format for arguments tup
52. address space offset integer Offset in bytes of the address or register from which to read Return values 4 3 Legacy API 75 PyVISA Documentation Release 1 5 value_8 value_16 value_32 integer Data read from bus 8 bits for in_8 16 bits for in_16 and 32 bits for in_32 install_handler Install handlers for event callbacks A handler must have the following signature def event_handler vi vent_type context user_handle Its parameters mean the following vi integer Unique logical identifier to a session event_type ViEvent Logical event identifier With event_type value you get its value as an integer context ViEvent A handle specifying the unique occurrence of an event user_handle ctypes pointer type A pointer to the user handle in ctypes form See below at Return values for how to use it however you have to substitute user_handle contents for converted_user_handle in the explanation Call converted_user_handle install_handler vi event_type handler user_handle VISA name vilnstallHandler Parameters vi integer Unique logical identifier to a session event_type integer Logical event identifier handler callable Interpreted as a valid reference to a handler to be installed by a client application user_handle None float integer string or list of floats or integers optional A value specified by an application that can be used for identifying handlers uniquely for an event typ
53. ameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session request_type_bitmap_field bmRequestType parameter of the setup stage of a USB con trol transfer e request_id bRequest parameter of the setup stage of a USB control transfer e request_value wValue parameter of the setup stage of a USB control transfer e index wIndex parameter of the setup stage of a USB control transfer This is usually the index of the interface or endpoint e length wLength parameter of the setup stage of a USB control transfer This value also specifies the size of the data buffer to receive the data from the optional data stage of the control transfer Returns The data buffer that receives the data from the optional data stage of the control transfer Return type bytes pyvisa ctwrapper functions usb_control_out library session request_type_bitmap_field request_id request_value index data u Performs a USB control pipe transfer to the device Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session request_type_bitmap_field bmRequestType parameter of the setup stage of a USB con trol transfer e request_id bRequest parameter of the setup stage of a USB control transfer e request_value wValue parameter of the setup stage of a USB control transfer e index wIndex parameter of the setup stag
54. ameters library_path path of the VISA library assert_interrupt_signal library session mode status_id Asserts the specified interrupt or signal Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e mode How to assert the interrupt Constants ASSERT e status_id This is the status value to be presented during an interrupt acknowledge cycle assert_trigger library session protocol Asserts software or hardware trigger Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e protocol Trigger protocol to use during assertion Constants PROT assert_utility signal library session line Asserts or deasserts the specified utility bus signal Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e line specifies the utility bus signal to assert Constants UTIL_ASSERT 3 4 API 23 PyVISA Documentation Release 1 5 buffer_read library session count Reads data from device or interface through the use of a formatted I O read buffer Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e count Number of bytes to be read Returns data read Return type bytes buffer_write library session data Writes data to a formatted I O write buffer syn
55. ary session space offset length data extended False Moves an 8 bit block of data from local memory to the specified address space and offset Parameters e library the visa library wrapped by ctypes session Unique logical identifier to a session space Specifies the address space Constants SPACE offset Offset in bytes of the address or register from which to read length Number of elements to transfer where the data width of the elements to transfer 1s identical to the source data width 3 4 API 31 PyVISA Documentation Release 1 5 e data Data to write to bus e extended Use 64 bits offset independent of the platform Corresponds to viMoveOut8 functions of the visa library open library session resource_name access_mode 0 open_timeout 0 Opens a session to the specified resource Parameters library the visa library wrapped by ctypes session Resource Manager session should always be a session returned from open_default_resource_manager resource_name Unique symbolic name of a resource access_mode Specifies the mode by which the resource is to be accessed Con stants NULL or Constants LOCK open_timeout Specifies the maximum time period in milliseconds that this operation waits before returning an error Returns Unique logical identifier reference to a session open_default_resource_manager library This function returns a
56. chronously Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e data bytes data to be written Returns number of written bytes clear library session Clears a device Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session close library session Closes the specified session event or find list Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session event or find list disable event library session event_type mechanism Disables notification of the specified event type s via the specified mechanism s Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e event_type Logical event identifier e mechanism Specifies event handling mechanisms to be disabled Constants QUEUE Handler SUSPEND_HNDLR ALL_MECH discard_events library session event_type mechanism Discards event occurrences for specified event types and mechanisms in a session Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session 24 Chapter 3 More information PyVISA Documentation Release 1 5 e event_type Logical event identifier e mechanism Specifies event handling mechanisms to be disabled Constants
57. ctypes e session Unique logical identifier to a session e address Source address to read the value Returns Data read from bus Return type bytes peek_32 library session address Read an 32 bit value from the specified address Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e address Source address to read the value Returns Data read from bus Return type bytes peek_8 library session address Read an 8 bit value from the specified address Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e address Source address to read the value Returns Data read from bus Return type bytes 3 4 API 33 PyVISA Documentation Release 1 5 poke_16 library session address data Write an 16 bit value from the specified address Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e address Source address to read the value e data value to be written to the bus Returns Data read from bus poke_32 library session address data Write an 32 bit value from the specified address Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e address Source address to read the value e data value to be written to the bus Returns Data read from
58. device interrupt or signal Call assert_interrupt_signal vi mode status_id VISA name viAssertIntrSignal Parameters vi integer Unique logical identifier to a session mode integer This specifies how to assert the interrupt status_id integer This is the status value to be presented during an interrupt acknowledge cycle Return values None assert_trigger Assert software or hardware trigger Call assert_trigger vi protocol VISA name viAssertTrigger Parameters vi integer Unique logical identifier to a session protocol integer Trigger protocol to use during assertion Valid values are VI_TRIG_PROT_DEFAULT VI_TRIG_PROT_ON VI_TRIG_PROT_OFF and VI_TRIG_PROT_SYNC Return values None assert_utility_signal Asserts the specified utility bus signal Call assert_utility_signal vi line VISA name viAssertUtilSignal Parameters vi integer Unique logical identifier to a session line integer Specifies the utility bus signal to assert Return values None 70 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 buffer_read Similar to read except that the operation uses the formatted I O read buffer for holding data read from the device Call buffer buffer_read vi count VISA name viBufRead Parameters vi integer Unique logical identifier to a session count integer Maximal number of bytes to be read Return values buffer string The buffer with the received data from device
59. e The VISA functions need to know what session you are referring to PyVISA opens exactly one session for each instrument or interface and stores its session handle in the instance attribute vi For example these two lines are equivalent my_instrument clear vpp43 clear my_instrument vi In case you need the session handle for the default resource manager it s stored in resource_manager session from visa import x from pyvisa import vpp43 my_instrument_handle vpp43 open resource_manager session GPIB 14 VI_EXCLUSIVE_LOCK Setting the VISA library in the program You can also set the path to your VISA library at the beginning of your program Just start the program with from pyvisa vpp43 import visa_library visa_library load_library usr lib libvisa so 7 from visa import x Keep in mind that the backslashes of Windows paths must be properly escaped or the path must be preceeded by r from pyvisa vpp43 import visa _library visa_library load_library r c WINNT system32 visa32 dll from visa import x 4 3 Legacy API 69 PyVISA Documentation Release 1 5 4 3 9 legacy vpp43 functions Please note that all descriptions given in this reference serve mostly as reminders For real descriptions consult a VISA specification or NI VISA Programmer Reference Manual However whenever there are PyVISA specific semantics they are listed here too assert_interrupt_signal Asserts the specified
60. e It defaults to None Return values converted_user_handle ctypes type An object representing the user_handle Use it to com municate with your handler If your user_handle was a list you get its elements as usual with converted_user_handle index You can even convert it to a list with list converted_user_handle however this yields a copy For strings use converted_user_handle value if it s supposed to be interpreted as a null terminated string or converted_user_handle raw if you want to see all bytes You can also write to both expressions however slicing is only possible for reading For simple types you can say converted_user_handle value read and write Attention You must assure that you never write values to converted_user_data which are longer in bytes than the initial values So be careful not to write a string longer than the original one nor a longer list You d be alerted by exceptions though lock Establish an access mode to the specified resource Call access_key lock vi lock_type timeout requested_key VISA name viLock 76 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 Parameters vi integer Unique logical identifier to a session lock_type integer Specifies the type of lock requested which can be either VI_EXCLUSIVE_LOCK or VI_SHARED_LOCK timeout integer Absolute time period in milliseconds that a resource waits to get unlocked by the locking se
61. e of course Return values None find_next Call instrument_ description find_next find_list VISA name viFindNext Parameters find_list ViFindList Describes a find list This parameter must be created by find_resources Return values instrument_description string Returns a string identifying the location of a device Strings can then be passed to open to establish a session to the given device find_resources Call find_list return_counter instrument_description find_resources session regular_expression VISA name viFindRsrc Parameters session integer Resource Manager session should always be the Default Resource Manager for VISA returned from open_default_resource_manager regular_expression integer This is a regular expression followed by an optional logical expres sion Return values find_list ViFindList Returns a handle identifying this search session This handle will be used as an input in find_next return_counter integer Number of matches instrument_description string Returns a string identifying the location of a device Strings can then be passed to open to establish a session to the given device flush Manually flush the specified buffers associated with formatted I O operations and or serial communication Call flush vi mask VISA name viFlush Parameters vi integer Unique logical identifier to a session mask integer Specifies the action to be taken with flushing the buffer
62. e all instruments connected with the computer The boolean use_aliases is True by default which means that the more human friendly aliases like COM1 instead of ASRLI are returned With some VISA systems you can define your own aliases for each device e g keithley617 for GPIBO 15 INSTR If use_aliases is False only standard resource names are returned instrument resource_name keyw returns an instrument variable for the instrument given by resource_name It saves you from calling one of the instrument classes directly by choosing the right one according to the type of the instrument So you have one function to open all of your instruments 4 3 Legacy API 63 PyVISA Documentation Release 1 5 The parameter resource_name may be any valid VISA instrument resource name see section VISA resource names In particular you can use a name returned by get_instruments_list above All further keyword arguments given to this function are passed to the class constructor of the respective instru ment class See section General devices for a table with all allowed keyword arguments and their meanings 4 3 2 Module classes General devices class Instrument resource_namel keyw represents an instrument e g a measurement device It is independent of a particular bus system i e it may be a GPIB serial USB or whatever instrument However it is not possible to perform bus specific operations on instrumen
63. e of a USB control transfer This is usually the index of the interface or endpoint e data The data buffer that sends the data in the optional data stage of the control transfer pyvisa ctwrapper functions vxi_command_query library session mode command Sends the device a miscellaneous command or query and or retrieves the response to a previous query Parameters 56 Chapter 3 More information PyVISA Documentation Release 1 5 e library the visa library wrapped by ctypes e session Unique logical identifier to a session e mode Specifies whether to issue a command and or retrieve a response Con stants VXI_CMD VXI_RESP e command The miscellaneous command to send Returns The response retrieved from the device pyvisa ctwrapper functions wait_on_ event library session in_event_type timeout Waits for an occurrence of the specified event for a given session Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e in_event_type Logical identifier of the event s to wait for e timeout Absolute time period in time units that the resource shall wait for a specified event to occur before returning the time elapsed error The time unit is in milliseconds Returns Logical identifier of the event actually received A handle specifying the unique occurrence of an event pyvisa ctwrapper functions write library session data
64. e of the ATN line and the local active controller state Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e mode Specifies the state of the ATN line and optionally the local active controller state Constants GPIB_ATN gpib_control_ren library session mode Controls the state of the GPIB Remote Enable REN interface line and optionally the remote local state of the device Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e mode Specifies the state of the REN line and optionally the device remote local state Constants GPIB_REN gpib_pass_control library session primary_address secondary_address Tell the GPIB device at the specified address to become controller in charge CIC Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e primary_address Primary address of the GPIB device to which you want to pass con trol 26 Chapter 3 More information PyVISA Documentation Release 1 5 e secondary_address Secondary address of the targeted GPIB device If the targeted device does not have a secondary address this parameter should contain the value Con stants NO_SEC_ADDR gpib_send_ifc library session Pulse the interface clear line IFC for at least 100 microseconds Parameters e library the
65. ent applica tion user_handle ctypes type optional A value specified by an application that can be used for iden tifying handlers uniquely in a session for an event It must be the object returned by in stall_handler Consequently it defaults to None Return values None unlock Relinquish a lock for the specified resource Call unlock vi VISA name viUnlock Parameters vi integer Unique logical identifier to a session Return values None unmap_address Unmap memory space previously mapped by map_address Call unmap_address vi VISA name viUnmapAddress 88 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 Parameters vi integer Unique logical identifier to a session Return values None unmap_trigger Undo a previous map from the specified trigger source line to the specified destination line Call unmap_trigger vi trigger_source trigger_destination VISA name viUnmapTrigger Parameters vi integer Unique logical identifier to a session trigger_source integer Source line used in previous map trigger_destination integer Destination line used in previous map Return values None usb_control_in Request arbitrary data from the USB device on the control port Call buffer usb_control_in vi request_type_bitmap_field request_id request_value index length VISA name viUsbControlIn Parameters vi integer Unique logical identifier to a session request_type_bitmap_field intege
66. ent signals an SRQ only this instrument The timeout argument given in seconds denotes the maximal waiting time The default value is 25 seconds If you pass None for the timeout this method waits forever if no SRQ arrives 2 5 Instruments 13 PyVISA Documentation Release 1 5 class Gpib board_number represents a GPIB board Although most setups have at most one GPIB interface card or USB GPIB device with board number 0 theoretically you may have more Be that as it may for board level operations i e operations that affect the whole bus with all connected devices you must create an instance of this class The optional GPIB board number board_number defaults to 0 The class Gp ib defines the following method Gpib send_ifc pulses the interface clear line IFC for at least 0 1 seconds Note You needn t store the board instance in a variable Instead you may send an IFC signal just by saying Gpib send_ifc 2 5 5 Serial devices Please note that serial instrument means only RS232 and parallel port instruments i e everything attached to COM and LPT In particular it does not include USB instruments For USB you have to use Inst rument instead class SerialInstrument resource_namel keyw represents a serial instrument resource_name is the VISA resource name see section VISA resource names The general keyword arguments are interpreted the same as with the class Instrument The only dif
67. entifier to a session e trigger_source Source line used in previous map Constants TRIG e trigger_destination Destination line used in previous map Constants TRIG usb_control_in library session request_type_bitmap_field request_id request_value index length 0 Performs a USB control pipe transfer from the device 36 Chapter 3 More information PyVISA Documentation Release 1 5 Parameters library the visa library wrapped by ctypes session Unique logical identifier to a session request_type_bitmap_field bmRequestType parameter of the setup stage of a USB con trol transfer request_id bRequest parameter of the setup stage of a USB control transfer request_value wValue parameter of the setup stage of a USB control transfer index wIndex parameter of the setup stage of a USB control transfer This is usually the index of the interface or endpoint length wLength parameter of the setup stage of a USB control transfer This value also specifies the size of the data buffer to receive the data from the optional data stage of the control transfer Returns The data buffer that receives the data from the optional data stage of the control transfer Return type bytes usb_control_out library session request_type_bitmap_field request_id request_value index data u Performs a USB control pipe transfer to the device Parameters e library the visa library wrapped by
68. er must detect when the device is finished with sending a message It does so by using different methods depending on the bus system In most cases you don t need to worry about termination characters because the defaults are very good However if you have trouble you may influence termination characters with PyVISA Termination characters may be one character or a sequence of characters Whenever this character or sequence occurs in the input stream the read operation is terminated and the read message is given to the calling application The next read operation continues with the input stream immediately after the last termination sequence In PyVISA the termination characters are stripped off the message before it is given to you You may set termination characters for each instrument e g my_instrument term_chars CR Alternatively you can give it when creating your instrument object my_instrument instrument GPIB 10 term_chars CR The default value depends on the bus system Generally the sequence is empty in particular for GPIB For RS232 its CR oy Well the real default is not the empty string but None There is a subtle difference really means the termina tion characters are not used at all neither for read nor for write operations In contrast None means that every write operation is implicitly terminated with CR LF This works well with most instruments All CRs and LFs are stripped from t
69. er to a session pyvisa ctwrapper functions close library session Closes the specified session event or find list Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session event or find list pyvisa ctwrapper functions disable event library session event_type mechanism Disables notification of the specified event type s via the specified mechanism s Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session 3 4 API 43 PyVISA Documentation Release 1 5 e event_type Logical event identifier e mechanism Specifies event handling mechanisms to be disabled Constants QUEUE Handler SUSPEND_HNDLR ALL_MECH pyvisa ctwrapper functions discard_events library session event_type mechanism Discards event occurrences for specified event types and mechanisms in a session Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e event_type Logical event identifier e mechanism Specifies event handling mechanisms to be disabled Constants QUEUE Handler SUSPEND_HNDLR ALL_MECH pyvisa ctwrapper functions enable event library session event_type mechanism con text 0 Enable event occurrences for specified event types and mechanisms in a session Parameters e library the visa library wrapped by ctypes
70. ference 1s the default value for term_chars For serial instruments CR carriage return is used to terminate readings and writings Note Since this class is derived from the class Instrument please refer to section General devices for all opera tions SerialInstrument can do everything that Instrument can do The class SerialInstrument defines the following additional properties Note that all properties can also be given as keyword arguments when calling the class constructor or instrument SerialInstrument baud_rate The communication speed in baud The default value is 9600 SerialInstrument data_bits Number of data bits contained in each frame Its value must be from 5 to 8 The default is 8 SerialInstrument stop_bits Number of stop bits contained in each frame Possible values are 1 1 5 and 2 The default is 1 SerialInstrument parity The parity used with every frame transmitted and received Possible values are Value Description no_parity no parity bit is used odd_parity the parity bit causes odd parity even_parity the parity bit causes even parity mark_parity the parity bit exists but it s always 1 space_parity the parity bit exists but it s always 0 The default value is no_parity SerialInstrument end_ input This determines the method used to terminate read operations Possible values are 14 Chapter 2 User guide PyVISA Documentation Release 1 5
71. from bus Return type bytes pyvisa ctwrapper functions poke_16 library session address data Write an 16 bit value from the specified address Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e address Source address to read the value e data value to be written to the bus Returns Data read from bus pyvisa ctwrapper functions poke_32 library session address data Write an 32 bit value from the specified address Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e address Source address to read the value e data value to be written to the bus Returns Data read from bus pyvisa ctwrapper functions poke_8 library session address data Write an 8 bit value from the specified address Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e address Source address to read the value e data value to be written to the bus Returns Data read from bus pyvisa ctwrapper functions read library session count Reads data from device or interface synchronously Parameters 3 4 API 53 PyVISA Documentation Release 1 5 e library the visa library wrapped by ctypes e session Unique logical identifier to a session e count Number of bytes to be read Returns data read Return type bytes
72. fter each write operation see section Termination characters Default O lock whether you want to have exclusive access to the device Default VI_NO_LOCK For further information about the locking mechanism see The VISA library implementation The class Instrument defines the following methods and attributes Instrument write message writes the string message to the instrument Instrument read returns a string sent from the instrument to the computer Instrument read_ values format returns a list of decimal values floats sent from the instrument to the computer See section A more complex example above The list may contain only one element or may be empty The optional format argument overrides the setting of values_format For information about that see section Reading binary data Instrument ask message sends the string message to the instrument and returns the answer string from the instrument Instrument ask_for_values messagel format sends the string message to the instrument and reads the answer as a list of values just as read_values does The optional format argument overrides the setting of values_format For information about that see section Reading binary data Instrument clear resets the device This operation is highly bus dependent I refer you to the original VISA documentation which explains how this is achieved for VXI GPIB serial etc Instrument trigger sends a tr
73. gs keithley write trace feed sensel feed control next Okay now the instrument is prepared to do the measurement The next three lines make the instrument waiting for a trigger pulse trigger it and wait until it sends a service request keithley write initiate keithley trigger keithley wait_for_srq With sending the service request the instrument tells us that the measurement has been finished and that the results are ready for transmission We could read them with keithley ask trace data however then we d get NDCV 000 0004E 0 NDCV 000 0005E 0 NDCV 000 0004E 0 NDCV 000 0007E 0 NDCV 000 0000E 0 NDCV 000 0007E 0 NDCV 000 0008E 0 NDCV 000 0004E 0 NDCV 000 0002E 0 NDCV 000 0005E 0 which we would have to convert to a Python list of numbers Fortunately the ask_for_values method does this work for us voltages keithley ask_for_values trace data print Average voltage sum voltages len voltages Finally we should reset the instrument s data buffer and SRQ status register so that it s ready for a new run Again this is explained in detail in the instrument s manual keithley ask status measurement keithley write trace clear feed control next That s it 18 lines of lucid code Well SCPI is awkward but that s another story 4 1 4 VISA resource names If you use the function instrument you must tell this function the VISA resource name of
74. he end of a read string no matter how term_chars is set The termination characters sequence is an ordinary string CR and LF are just string constants that allow readable access to W and WM Therefore instead of CR LF you can also write w whichever you like more 68 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 delay and send_end There are two further options related to message termination namely send_end and delay send_end is a boolean If it s True the default the EOI line is asserted after each write operation signalling the end of the operation EOI is GPIB specific but similar action is taken for other interfaces The argument delay is the time in seconds to wait after each write operation So you could write my_instrument instrument GPIB 10 send_end False delay 1 2 This will set the delay to 1 2 seconds and the EOI line is omitted By the way omitting EOI is not recommended so if you omit it nevertheless you should know what you re doing 4 3 8 Mixing with direct VISA commands You can mix the high level object oriented approach described in this document with middle level VISA function calls in module vpp43 as described in The VISA library implementation which is also part of the PyVISA package By doing so you have full control of your devices I recommend to import the VISA functions with from pyvisa import vpp43 Then you can use them with vpp43 function_nam
75. he platform Returns Data read from memory install_handler session event_type handler user_handle None Installs handlers for event callbacks Parameters 3 4 API 27 PyVISA Documentation Release 1 5 session Unique logical identifier to a session event_type Logical event identifier handler Interpreted as a valid reference to a handler to be installed by a client applica tion user_handle A value specified by an application that can be used for identifying handlers uniquely for an event type Returns user handle a ctypes object lock library session lock_type timeout requested_key None Establishes an access mode to the specified resources Parameters library the visa library wrapped by ctypes session Unique logical identifier to a session lock_type Specifies the type of lock requested either Constants EXCLUSIVE_LOCK or Constants SHARED_LOCK timeout Absolute time period in milliseconds that a resource waits to get unlocked by the locking session before returning an error requested_key This parameter is not used and should be set to VI_NULL when lock Type is VI EXCLUSIVE_LOCK Returns access_key that can then be passed to other sessions to share the lock map_address library session map_space map_base map_size access 0 suggested 0 Maps the specified memory space into the process s address space Parameters e library the visa librar
76. hich to write destination_width integer Specifies the data width of the destination length integer Number of elements to transfer where the data width of the elements to transfer is identical to source data width Return values job_id ViJobld The job identifier of this asynchronous move operation Each time an asyn chronous move operation is called it is assigned a unique job identifier move_in_8 move_in_16 move_in_32 Move a block of data from the specified address space and offset to local memory in increments of 8 16 or 32 bits Call buffer_8 move_in_8 vi space offset length buffer_16 move_in_16 vi space offset length buffer_32 move_in_32 vi space offset length VISA name viMoveln8 viMoveln16 viMoveln32 Parameters vi integer Unique logical identifier to a session space integer Specifies the address space offset ViBusAddress Offset in bytes of the starting address or register from which to read length integer Number of elements to transfer where the data width of the elements to transfer is identical to data width 8 16 or 32 bits Return values buffer_8 buffer_16 buffer_32 list of integers Data read from bus as a Python list of values 4 3 Legacy API 79 PyVISA Documentation Release 1 5 move_out_8 move _out_16 move_out_32 Move a block of data from local memory to the specified address space and offset in increments of 8 16 or 32 bits Call move_out_8 vi
77. ienced this effect with my National Instru ments VISA implementation which rounds off to 0 1 3 and 10 seconds 4 3 5 Chunk length If you read data from a device you must store it somewhere Unfortunately PyVISA must make space for the data before it starts reading which means that it must know how much data the device will send However it doesn t know a priori Therefore PyVISA reads from the device in chunks Each chunk is 20 kilobytes long by default If there s still data to be read PyVISA repeats the procedure and eventually concatenates the results and returns it to you Those 20 kilobytes are large enough so that mostly one read cycle is sufficient The whole thing happens automatically as you can see Normally you needn t worry about it However some devices don t like to send data in chunks So if you have trouble with a certain device and expect data lengths larger than the default chunk length you should increase its value by saying e g my_instrument chunk_size 102400 This example sets it to 100 kilobytes 4 3 6 Reading binary data Some instruments allow for sending the measured data in binary form This has the advantage that the data transfer is much smaller and takes less time PyVISA currently supports three forms of transfers ascii This is the default mode It assumes a normal string with comma or whitespace separated values single The values are expected as a binary sequence of IEEE floating point
78. if you do not have VISA installed 18 Chapter 3 More information PyVISA Documentation Release 1 5 e a CFFI based wrapper CFFI is new python package that allows easier and more robust wrapping of foreign libraries It might be part of Python in the future PyVISA 1 5 keeps vpp43 in the legacy subpackage reimplemented on top of ctwrapper to help with the migration but it will be removed in the future All functions that were present in vpp43 are now present in ctwrapper but they take an additional first parameter the foreign library wrapper We suggest that you replace vpp43 by using the new VisaLibrary object which provides all foreign functions as bound methods see below No singleton objects The original Py VISA implementation relied on a singleton global objects for the library wrapper named visa_library an instance of the old pyvisa vpp43 VisaLibrary and the resource manager named resource_manager and instance of the old pyvisa visa ResourceManager These were instantiated on import and the user could rebind to a different library using the load_library method Calling this method however did not affect resource_manager and might lead to an inconsistent state In 1 5 there is a new VisaLibrary class and a new ResourceManager class they are both in pyvisa highlevel The new classes are not singletons at least not in the strict sense Multiple instances of VisaLibrary and ResourceManager are possible but only if
79. igger signal to the instrument Instrument read_raw returns a string sent from the instrument to the computer In contrast to read no termination characters are checked or stripped You get the pristine message 10 Chapter 2 User guide PyVISA Documentation Release 1 5 Instrument timeout The timeout in seconds for each I O operation See section Timeouts for further information Instrument term_chars The termination characters for each read and write operation See section Termination characters for further information Instrument send_end Whether or not to assert EOI or something equivalent depending on the interface type after each write opera tion See section Termination characters for further information Instrument delay Time in seconds to wait after each write operation See section Termination characters for further information Instrument values_format The format for multi value data sent from the instrument to the computer See section Reading binary data for further information 2 5 1 Common properties of instrument variables Timeouts Very most VISA I O operations may be performed with a timeout If a timeout is set every operation that takes longer than the timeout is aborted and an exception is raised Timeouts are given per instrument For all PyVISA objects a timeout is set with my_device timeout 25 Here my_device may be a device an interface or whatever and its timeout is set
80. ination characters for further information Instrument send_end Whether or not to assert EOI or something equivalent depending on the interface type after each write opera tion See section Termination characters for further information Instrument delay Time in seconds to wait after each write operation See section Termination characters for further information Instrument values_format The format for multi value data sent from the instrument to the computer See section Reading binary data for further information GPIB devices class GpibInstrument gpib_identifier board_numberl keyw 1 represents a GPIB instrument If gpib_identifier is a string it is interpreted as a VISA resource name section VISA resource names If it is a number it denotes the device number at the GPIB bus The optional board_number defaults to zero If you have more that one GPIB bus system attached to the computer you can select the bus with this parameter The keyword arguments are interpreted the same as with the class Instrument Note Since this class is derived from the class Inst rument please refer to section General devices for the basic operations GpibInstrument can do everything that Instrument can do so it simply extends the original class with GPIB specific operations The class GpibInstrument defines the following methods GpibInstrument wait_for_srq timeout waits for a serial request SRQ coming from the instr
81. ions set_signatures library errcheck None Set the signatures of most visa functions in the library All instrumentation related functions are specified here String related functions such as viPrintf require a cdecl calling convention even in windows and therefore are require a CDLL object See set_cdecl_signatures Parameters library ctypes WinDLL or ctypes CDLL the visa library wrapped by ctypes e errcheck error checking callable used for visa functions that return ViStatus It should be take three areguments result func arguments See errcheck in ctypes pyvisa ctwrapper functions set_cdecl_signatures clibrary errcheck None Set the signatures of visa functions requiring a cdecl calling convention Parameters e clibrary ctypes CDLL the visa library wrapped by ctypes e errcheck error checking callable used for visa functions that return ViStatus It should be take three areguments result func arguments See errcheck in ctypes pyvisa ctwrapper functions assert_interrupt_signal library session mode status_id Asserts the specified interrupt or signal Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e mode How to assert the interrupt Constants ASSERT e status_id This is the status value to be presented during an interrupt acknowledge cycle pyvisa ctwrapper functions assert_trigger library session protocol Asser
82. ite_format 86 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 buffer_length integer keyword argument Length of the user specified buffer in bytes Defaults to 1024 Return values buffer string Buffer where the formatted data was written to sscanf Same as scanf except that the data is read from a user specified buffer instead of a device Warning The current implementation only supports the following C data types Long double and char strings Thus you can only use these three data types in format strings for printf scanf and the like Call valuel value2 sscanf vi buffer read_format maximal_string_length 1024 VISA name viSScanf Parameters vi integer Unique logical identifier to a session buffer string Buffer from which data is read and formatted read_format string String describing the format for arguments integers floats or strings Arguments to be read from the device according to read_format It s totally insignificant which values they have they serve just as a cheap way to determine what types are to be expected So actually this argument list shouldn t be necessary but with the current implementation it 1s sorry These arguments may be however needn t be the same names used for storing the result values Alternatively you can give literals maximal_string_length integer keyword argument The maximal length assumed for string result argumen
83. iven resource string interface_board_number integer Board number of the interface of the given resource string resource_class string Specifies the resource class for example INSTR of the given resource string unaliased_expanded_resource_name string This is the expanded version of the given resource string The format should be similar to the VISA defined canonical resource name alias_if_exists string Specifies the user defined alias for the given resource string if a VISA im plementation allows aliases and an alias exists for the given resource string If not this is None peek_8 peek_16 peek_32 Read an 8 bit 16 bit or 32 bit value from the specified address Call value_8 peek_8 vi address value_16 peek_16 vi address value_32 peek_32 vi address VISA name viPeek8 viPeek16 viPeek32 Parameters vi integer Unique logical identifier to a session address ViAddr Specifies the source address to read the value Return values value_8 value_16 value_32 integer Data read from bus 8 bits for peek_8 16 bits for peek_16 and 32 bits for peek_32 poke_8 poke_16 poke_32 Write an 8 bit 16 bit or 32 bit value to the specified address Call 82 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 poke_8 vi address value_8 poke_16 vi address value_16 poke_32 vi address value_32 VISA name vipoke_8 Parameters vi integer Unique logical identifier to a session
84. ke a look at AUTHORS for more information 3 3 3 found a bug how can report it Please report it on the Issue Tracker including operating system python version and library version In addition you might add supporting information by pasting the output of this command python c from pyvisa import util util get_debug_info 3 3 4 Error Image not found This error occurs when you have provided an invalid path for the VISA library Check that the path provided to the constructor or in the configuration file 3 3 5 Error Could not found VISA library This error occurs when you have not provided a path for the VISA library and PyVISA is not able to find it for you You can solve it by providing the library path to the VisaLibrary or ResourceManager constructor gt gt gt visalib VisaLibrary path to library or gt gt gt rm ResourceManager Path to library or by create a configuration file as described in ref configuring 3 3 6 Error No matching architecture This error occurs when you the Python architecture does not match the VISA architecture Note PyVISA tries to parse the error from the underlying foreign function library to provide a more useful error message If it does not succeed it shows the original one In Mac OS X the original error message looks like this 3 3 Frequently asked questions 21 PyVISA Documentation Release 1 5 OS Error dlopen Library Framewor
85. ks visa framework visa 6 no suitable image found Did find Library Frameworks visa framework visa no matching architecture in universal wrapper Library Frameworks visa framework visa no matching architecture in universal wrapper In Linux the original error message looks like this OS Error Could not open VISA library Error while accessing usr local vxipnp linux bin libvisa so 7 usr local vxipnp linux bin libvi First determine the details of your installation with the help of the following debug command python c from pyvisa import util util get_debug_info You will see the bitness of the Python interpreter and at the end you will see the list of VISA libraries that PyVISA was able to find The solution is to or 1 Install and use a VISA library matching your Python bitness Download and install it from National Instruments s VISA Run the debug command again to see if the new library was found by PyVISA If not create a configuration file as described in ref configuring If there is no VISA library with the correct bitness available try solution 2 Install and use a Python matching your VISA library bitness In Windows and Linux Download and install Python with the matching bitness Run your script again using the new Python In Mac OS X Python is usually delivered as universal binary 32 and 64 bits You can run it in 32 bit by running arch i386 python myscript py
86. ld classes Parameters e resource_name the instrument s resource name or an alias may be taken from the list from list_resources method from a ResourceManager e timeout the VISA timeout for each low level operation in milliseconds e term_chars the termination characters for this device e chunk_size size of data packets in bytes that are read from the device e lock whether you want to have exclusive access to the device Default VI_LNO_LOCK e ask_delay waiting time in seconds after each write command Default 0 0 e send_end whether to assert end line after each write command Default True e values_format floating point data value format Default ascii 0 ask message delay None A combination of write message and read Parameters e message str the message to send e delay delay in seconds between write and read operations if None defaults to self ask_delay Returns the answer from the device 3 4 API 39 PyVISA Documentation Release 1 5 Return type str ask_for_values message format None delay None A combination of write message and read_values Parameters e message str the message to send e delay delay in seconds between write and read operations if None defaults to self ask_delay Returns the answer from the device Return type list encoding Encoding used for read and write operations read termination None encoding None Read
87. le of integers floats or strings Arguments sent to the device according to write_format May be None 4 3 Legacy API 83 PyVISA Documentation Release 1 5 integers floats or strings Arguments to be read from the device according to read_format It s totally insignificant which values they have they serve just as a cheap way to determine what types are to be expected So actually this argument list shouldn t be necessary but with the current implementation it 1s sorry These arguments may be however needn t be the same names used for storing the result values Alternatively you can give literals maximal_string_length integer keyword argument The maximal length assumed for string result arguments Note that string results must never exceed this length It defaults to 1024 Return values valuel value2 integers floats or strings Arguments read from the device according to read_format Of course this must be the same sequence as far as data types are concerned as the given argument list above read Read data from device synchronously Call buffer read vi count VISA name viRead Parameters vi integer Unique logical identifier to a session count integer Maximal number of bytes to be read Return values buffer string Represents the buffer with the received data from device read_asynchronously Read data from device asynchronously Call buffer job_id read_asynchronously vi
88. library path to my libvisa so 7 By default vpp43 looks for the library in usr local vxipnp linux bin libvisa so 7 Please pay attention to the fact that the library must have been successfully loaded before any VISA call is made Alternatively you can tell PyVISA so by creating a file pyvisarc This has the format of an INI file For example if the library is at usr lib libvisa so 7 the file pyvisarc must contain the following Paths VISA library usr lib libvisa so 7 Please note that Paths is treated case sensitively You can define a site wide configuration file at usr share pyvisa pyvisarc It may also be usr local depending on the location of your Python 62 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 4 2 2 Diagnostics This module can raise a couple of vpp43 specific exceptions Name VisalOError Description This is an error of the underlying VISA library as described in table 3 3 1 in the VISA specification for textual languages The exception member error_code contains the always negative VISA error number as listed in that table Name VisalOWarning Description This is a warning of the underlying VISA library as described in table 3 3 1 in the VISA specification for textual languages The exception member complet ion_code contains the al ways positive VISA completion number as listed in that table Normally you don t see these warnings You can turn them into e
89. list above set_attribute Set the state of an attribute Call set_attribute vi attribute attribute_state VISA name viSetAttribute Parameters vi integer ViEvent or ViFindList Unique logical identifier to a session attribute integer Session event or find list attribute for which the state is modified attribute_state integer The state of the attribute to be set for the specified resource The interpre tation of the individual attribute value is defined by the resource Return values None set_buffer Set the size for the formatted I O and or serial communication buffer s Call set_buffer vi mask size VISA name viSetBuf Parameters vi integer Unique logical identifier to a session mask integer Specifies the type of buffer size integer The size to be set for the specified buffer s Return values None sprintf Same as printf except the data is written to a user specified buffer rather than the device Warning The current implementation only supports the following C data types Long double and char strings Thus you can only use these three data types in format strings for printf scanf and the like Call buffer sprintf vi write_format buffer_length 1024 VISA name viSPrintf Parameters vi integer Unique logical identifier to a session write_format string String describing the format for arguments integers floats or strings Arguments sent to the buffer according to wr
90. n Unique logical identifier to a session e size Specifies the size of the allocation e extended Use 64 bits offset independent of the platform Returns Returns the offset of the allocated memory pyvisa ctwrapper functions memory_free library session offset extended False Frees memory previously allocated using the memory_allocation operation Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e offset Offset of the memory to free e extended Use 64 bits offset independent of the platform pyvisa ctwrapper functions move library session source_space source_offset source_width destination_space destination_offset destination_width length Moves a block of data Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e source_space Specifies the address space of the source e source_offset Offset of the starting address or register from which to read e source_width Specifies the data width of the source e destination_space Specifies the address space of the destination e destination_offset Offset of the starting address or register to which to write e destination_width Specifies the data width of the destination e length Number of elements to transfer where the data width of the elements to transfer is identical to the source data width 48
91. n signalling the end of the operation EOI is GPIB specific but similar action is taken for other interfaces The argument delay is the time in seconds to wait after each write operation So you could write my_instrument instrument GPIB 10 send_end False delay 1 2 This will set the delay to 1 2 seconds and the EOI line is omitted By the way omitting EOI is not recommended so if you omit it nevertheless you should know what you re doing 2 5 4 GPIB devices class GpibInstrument gpib_identifier board_numberl keyw 1 represents a GPIB instrument If gpib_identifier is a string it is interpreted as a VISA resource name section VISA resource names If it is a number it denotes the device number at the GPIB bus The optional board_number defaults to zero If you have more that one GPIB bus system attached to the computer you can select the bus with this parameter The keyword arguments are interpreted the same as with the class Instrument Note Since this class is derived from the class Inst rument please refer to section General devices for the basic operations Goib Instrument can do everything that Instrument can do so it simply extends the original class with GPIB specific operations The class GpibInstrument defines the following methods GpibInstrument wait_for_srq timeout waits for a serial request SRQ coming from the instrument Note that this method is not ended when another instrum
92. n bytes of the address or register from which to read length Number of elements to transfer where the data width of the elements to transfer is identical to the source data width data Data to write to bus 50 Chapter 3 More information PyVISA Documentation Release 1 5 e extended Use 64 bits offset independent of the platform Corresponds to viMoveOut32 functions of the visa library pyvisa ctwrapper functions move_out_8 library session space offset length data ex tended False Moves an 8 bit block of data from local memory to the specified address space and offset Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e space Specifies the address space Constants SPACE e offset Offset in bytes of the address or register from which to read e length Number of elements to transfer where the data width of the elements to transfer is identical to the source data width e data Data to write to bus e extended Use 64 bits offset independent of the platform Corresponds to viMoveOut8 functions of the visa library pyvisa ctwrapper functions open library session resource_name access_mode 0 open_timeout 0 Opens a session to the specified resource Parameters e library the visa library wrapped by ctypes e session Resource Manager session should always be a session returned from open_default_resource
93. nctions gpib_control_ren library session mode Controls the state of the GPIB Remote Enable REN interface line and optionally the remote local state of the device Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e mode Specifies the state of the REN line and optionally the device remote local state Constants GPIB_REN pyvisa ctwrapper functions gpib_pass_control library session primary_address sec ondary_address Tell the GPIB device at the specified address to become controller in charge CIC Parameters 3 4 API 45 PyVISA Documentation Release 1 5 library the visa library wrapped by ctypes session Unique logical identifier to a session primary_address Primary address of the GPIB device to which you want to pass control secondary_address Secondary address of the targeted GPIB device If the targeted device does not have a secondary address this parameter should contain the value Con stants NO_SEC_ADDR pyvisa ctwrapper functions gpib_send_ifc library session Pulse the interface clear line IFC for at least 100 microseconds Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session pyvisa ctwrapper functions in_16 library session space offset extended False Reads in an 16 bit value from the specified memory space and offset Parameters e lib
94. nstrument for the resource name Parameters e resource_name name or alias of the resource to open e kwargs keyword arguments to be passed to the instrument constructor list_resources query INSTR Returns a tuple of all connected devices matching query 38 Chapter 3 More information PyVISA Documentation Release 1 5 Parameters query regular expression used to match devices list_resources_info query INSTR Returns a dictionary mapping resource names to resource extended information of all connected devices matching query Parameters query regular expression used to match devices Returns Mapping of resource name to ResourceInfo Return type dict open_resource resource_name access_mode 0 open_timeout 0 Open the specified resources Parameters e resource_name name or alias of the resource to open e access_mode access mode e open_timeout time out to open Returns Unique logical identifier reference to a session resource info resource_name Get the extended information of a particular resource Parameters resource_name Unique symbolic name of a resource Return type ResourceInfo class pyvisa highlevel Instrument resource_name resource_manager None kwargs Class for all kinds of Instruments It can be instantiated however if you want to use special features of a certain interface system GPIB USB RS232 etc you must instantiate one of its chi
95. o a session param space Specifies the address space 3 4 API 51 PyVISA Documentation Release 1 5 Constants SPACE param offset Offset in bytes of the address or register from which to read param data Data to write to bus param extended Use 64 bits offset independent of the platform Corresponds to viOut32 functions of the visa library pyvisa ctwrapper functions out_8 library session space offset data extended False Write in an 8 bit value from the specified memory space and offset param library the visa library wrapped by ctypes param session Unique logical identifier to a session param space Specifies the address space Constants SPACE param offset Offset in bytes of the address or register from which to read param data Data to write to bus param extended Use 64 bits offset independent of the platform Corresponds to viOut8 functions of the visa library pyvisa ctwrapper functions parse_resource library session resource_name Parse a resource string to get the interface information Parameters e library the visa library wrapped by ctypes e session Resource Manager session should always be the Default Resource Manager for VISA returned from open_default_resource_manager e resource_name Unique symbolic name of a resource Returns Resource information with interface type and board number Return type class ResourceInfo pyvisa ctwrapper functions parse_resou
96. of the underlying implementation But you are encouraged to do a few things differently 1f you want to keep up with the latest developments and be compatible with PyVISA gt 1 5 Tf you are doing gt gt gt import visa gt gt gt keithley visa instrument GPIB 12 gt gt gt print keithley ask x IDN change it to gt gt gt import visa gt gt gt rm visa ResourceManager gt gt gt keithley rm get_instrument GPIB 12 gt gt gt print keithley ask IDN If you are doing gt gt gt print visa get_instruments_list change it to gt gt gt print rm list_resources If you are doing 17 PyVISA Documentation Release 1 5 gt gt gt import pyvisa vpp43 as vpp43 gt gt gt vpp43 visa_library load_library path to my libvisa so 7 change it to gt gt gt import visa gt gt gt lib visa VisaLibrary path to my libvisa so 7 If you are doing gt gt gt vpp43 lock session change it to gt gt gt lib lock session If you are doing gt gt gt inst term_chars Nr change it to gt gt gt inst read_termination r gt gt gt inst write_termination r As you see most of the code shown above is making a few things explict It adds line of code instantiating the VisaLibrary or ResourceManager object which is not a big deal but it makes things cleaner If you were using printf queryf scanf
97. of the visa library move_in_32 library session space offset length extended False Moves an 32 bit block of data from the specified address space and offset to local memory Parameters e library the visa library wrapped by ctypes session Unique logical identifier to a session space Specifies the address space Constants SPACE offset Offset in bytes of the address or register from which to read length Number of elements to transfer where the data width of the elements to transfer 1s identical to the source data width e extended Use 64 bits offset independent of the platform Returns Data read from bus Corresponds to viMoveln32 functions of the visa library move_in_8 library session space offset length extended False Moves an 8 bit block of data from the specified address space and offset to local memory Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e space Specifies the address space Constants SPACE e offset Offset in bytes of the address or register from which to read 30 Chapter 3 More information PyVISA Documentation Release 1 5 e length Number of elements to transfer where the data width of the elements to transfer 1s identical to the source data width e extended Use 64 bits offset independent of the platform Returns Data read from bus Corresponds to viMoveln8 func
98. on Return type unicode Py2 or str Py3 terminate library session degree job_id Requests a VISA session to terminate normal execution of an operation Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e degree Constants NULL e job_id Specifies an operation identifier uninstall_handler session event_type handler user_handle None Uninstalls handlers for events Parameters e session Unique logical identifier to a session e event_type Logical event identifier e handler Interpreted as a valid reference to a handler to be uninstalled by a client appli cation e user_handle A value specified by an application that can be used for identifying handlers uniquely in a session for an event unlock library session Relinquishes a lock for the specified resource Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session unmap_address library session Unmaps memory space previously mapped by map_address Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session unmap_trigger library session trigger_source trigger_destination Undo a previous map from the specified trigger source line to the specified destination line Parameters e library the visa library wrapped by ctypes e session Unique logical id
99. on list of numbers Fortunately the ask_for_values method does this work for us gt gt gt voltages keithley ask_for_values trace data gt gt gt print Average voltage sum voltages len voltages Finally we should reset the instrument s data buffer and SRQ status register so that it s ready for a new run Again this is explained in detail in the instrument s manual gt gt gt keithley ask status measurement gt gt gt keithley write trace clear feed control next That s it 18 lines of lucid code Well SCPI is awkward but that s another story 2 2 5 VISA resource names If you use the function get_instrument you must tell this function the VISA resource name of the instrument you want to connect to Generally it starts with the bus type followed by a double colon followed by the number within the bus For example GPIB 10 denotes the GPIB instrument with the number 10 If you have two GPIB boards and the instrument is connected to board number 1 you must write GPIB1 10 As for the bus things like GPIB USB ASRL for serial parallel interface are possible So for connecting to an instrument at COM2 the resource name is ASRL2 Since only one instrument can be connected with one serial interface there is no double colon parameter However most VISA systems allow aliases such as COM2 or LPTI You may also add your own aliases
100. operations and or serial communica tion Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e mask Specifies the action to be taken with flushing the buffer Constants READ WRITE IO classmethod from_paths paths Helper constructor that tries to instantiate VisaLibrary from an iterable of possible library paths get_attribute library session attribute Retrieves the state of an attribute 3 4 API 25 PyVISA Documentation Release 1 5 Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session event or find list attribute Resource attribute for which the state query is made see Attributes Returns The state of the queried attribute for a specified resource Return type unicode Py2 or str Py3 list or other type get_default_resource_manager library This function returns a session to the Default Resource Manager resource Parameters library the visa library wrapped by ctypes Returns Unique logical identifier to a Default Resource Manager session gpib_command library session data Write GPIB command bytes on the bus Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e data bytes data tor write Returns Number of written bytes gpib_control_atn library session mode Specifies the stat
101. ory into an address region different from suggested Return values address ViAddr Address in your process space where the memory was mapped map_trigger Map the specified trigger source line to the specified destination line Call map_trigger vi trigger_source trigger_destination mode VISA name viMapTrigger Parameters vi integer Unique logical identifier to a session trigger_source integer Source line from which to map 4 3 Legacy API 77 PyVISA Documentation Release 1 5 trigger_destination integer Destination line to which to map mode integer Specifies the trigger mapping mode This should always be VI_NULL Return values None memory_allocation Allocate memory from a device s memory region Call memory_allocation vi size VISA name viMemAlloc Parameters vi integer Unique logical identifier to a session size integer Specifies the size of the allocation Return values offset ViBusAddress Returns the offset of the allocated device memory memory_free Free memory previously allocated using memory_allocation Call memory_free vi offset VISA name viMemFree Parameters vi integer Unique logical identifier to a session offset ViBusAddress Specifies the memory previously allocated with memory_allocation Return values None move Move a block of data Call move vi source_space source_offset source_width destination_space destination_offset destina tion_width length
102. ple 59 PyVISA Documentation Release 1 5 from pyvisa legacy import visa my_instrument instrument GPIB 14 my_instrument write IDN print my_instrument read This example already shows the two main design goals of PyVISA preferring simplicity over generality and doing it the object oriented way Every instrument is represented in the source by an object instance In this case I have a GPIB instrument with instrument number 14 so I create the instance i e variable called my_instrument accordingly my_instrument instrument GPIB 14 GPIB 14 is the instrument s resource name See section VISA resource names for a short explanation of that Then I send the message IDN to the device which is the standard GPIB message for what are you or in some cases what s on your display at the moment my_instrument write IDN Finally I print the instrument s answer on the screen print my_instrument read 4 1 2 Example for serial RS232 device The only RS232 device in my lab is an old Oxford ITC4 temperature controller which is connected through COM2 with my computer The following code prints its self identification on the screen from pyvisa legacy import visa itc4 visa instrument COM2 itc4 write V print itc4 read Instead of separate write and read operations you can do both with one ask call Thus the above source code is equivalent to
103. ppens automatically as you can see Normally you needn t worry about it However some devices don t like to send data in chunks So if you have trouble with a certain device and expect data lengths larger than the default chunk length you should increase its value by saying e g my_instrument chunk_size 102400 This example sets it to 100 kilobytes 2 5 2 Reading binary data Some instruments allow for sending the measured data in binary form This has the advantage that the data transfer is much smaller and takes less time PyVISA currently supports three forms of transfers ascii This is the default mode It assumes a normal string with comma or whitespace separated values single The values are expected as a binary sequence of IEEE floating point values with single precision i e four bytes each All flavours of binary data streams defined in IEEE488 2 are supported i e those beginning with lt header gt lt digit gt where lt header gt is optional and lt digit gt may also be 0 double The same as single but with values of double precision eight bytes each You can set the form of transfer with the property values_format either with the generation of the object my_instrument instrument GPIB 12 values_format single or later by setting the property directly my_instrument values_format single Setting this option affects the methods read_values and ask_for_values In particular you must assure
104. preted the same as with the class Instrument The only difference 1s the default value for term_chars For serial instruments CR carriage return is used to terminate readings and writings Note Since this class is derived from the class Instrument please refer to section General devices for all opera tions SerialInstrument can do everything that Instrument can do The class SerialInstrument defines the following additional properties Note that all properties can also be given as keyword arguments when calling the class constructor or instrument SerialInstrument baud_rate The communication speed in baud The default value is 9600 SerialInstrument data_bits Number of data bits contained in each frame Its value must be from 5 to 8 The default is 8 SerialInstrument stop_bits Number of stop bits contained in each frame Possible values are 1 1 5 and 2 The default is 1 SerialInstrument parity The parity used with every frame transmitted and received Possible values are Value Description no_parity no parity bit is used odd_parity the parity bit causes odd parity even_parity the parity bit causes even parity mark_parity the parity bit exists but it s always 1 space_parity the parity bit exists but it s always 0 The default value is no_parity SerialInstrument end_input This determines the method used to terminate read operations Possible values are Value Description
105. r Bitmap field for defining the USB control port request The bitmap fields are as defined by the USB specification The direction bit must be device to host request_id integer Request ID for this transfer The meaning of this value depends on re quest_type_bitmap_field request_value integer Request value for this transfer index integer Specifies the interface or endpoint index number depending on re quest_type_bitmap_field length integer optional Number of data in bytes to request from the device during the Data stage If this value is not given or 0 an empty string is returned Return values buffer string Actual data received from the device during the Data stage If length is not given or 0 an empty string is returned usb_control_ out Send arbitrary data to the USB device on the control port Call usb_control_out vi request_type_bitmap_field request_id request_value index buffer VISA name viUsbControlOut 4 3 Legacy API 89 PyVISA Documentation Release 1 5 Parameters vi integer Unique logical identifier to a session request_type_bitmap_field integer Bitmap field for defining the USB control port request The bitmap fields are as defined by the USB specification The direction bit must be host to device request_id integer Request ID for this transfer The meaning of this value depends on re quest_type_bitmap_field request_value integer Request value for this transfer inde
106. rary the visa library wrapped by ctypes e session Unique logical identifier to a session e space Specifies the address space Constants SPACE e offset Offset in bytes of the address or register from which to read e extended Use 64 bits offset independent of the platform Returns Data read from memory pyvisa ctwrapper functions in_32 library session space offset extended False Reads in an 32 bit value from the specified memory space and offset Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e space Specifies the address space Constants SPACE e offset Offset in bytes of the address or register from which to read e extended Use 64 bits offset independent of the platform Returns Data read from memory pyvisa ctwrapper functions in_8 library session space offset extended False Reads in an 8 bit value from the specified memory space and offset Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e space Specifies the address space Constants SPACE e offset Offset in bytes of the address or register from which to read e extended Use 64 bits offset independent of the platform Returns Data read from memory 46 Chapter 3 More information PyVISA Documentation Release 1 5 pyvisa ctwrapper functions install_handler library ses
107. rce_extended library session resource_name Parse a resource string to get extended interface information Parameters e library the visa library wrapped by ctypes e session Resource Manager session should always be the Default Resource Manager for VISA returned from open_default_resource_manager e resource_name Unique symbolic name of a resource Returns Resource information Return type class ResourceInfo pyvisa ctwrapper functions peek_16 library session address Read an 16 bit value from the specified address Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e address Source address to read the value Returns Data read from bus Return type bytes pyvisa ctwrapper functions peek_32 library session address Read an 32 bit value from the specified address Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session 52 Chapter 3 More information PyVISA Documentation Release 1 5 address Source address to read the value Returns Data read from bus Return type bytes pyvisa ctwrapper functions peek_8 library session address Read an 8 bit value from the specified address Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e address Source address to read the value Returns Data read
108. return a dict mapping resource name to a namedtuple containing information such as the interface type and the resource class 2 2 3 Example for serial RS232 device There is no only RS232 device in my lab is an old Oxford ITC4 temperature controller which is connected through COM2 with my computer The following code prints its self identification on the screen itc4 rm get_instrument COM2 itc4 write V print itc4 read Instead of separate write and read operations you can do both with one ask call Thus the above source code is equivalent to from visa import x itc4 instrument COM2 print itc4 ask V It couldn t be simpler See section Serial devices for further information about serial devices 2 2 4 A more complex example The following example shows how to use SCPI commands with a Keithley 2000 multimeter in order to measure 10 voltages After having read them the program calculates the average voltage and prints it on the screen Pll explain the program step by step First we have to initialise the instrument gt gt gt keithley rm get_instrument GPIB 12 gt gt gt keithley write rst status preset cls Here we create the instrument variable keithley which is used for all further operations on the instrument Immediately after it we send the initialisation and reset message to the instrument The next step is to write all the measurement parameters in particular the interval
109. s contained in each frame from 5 to 8 end_input indicates the method used to terminate read operations parity The parity used with every frame transmitted and received stop_bits Number of stop bits contained in each frame 1 1 5 or 2 class pyvisa highlevel GpibInstrument gpib_identifier board_number 0 re source_manager None keyw Class for GPIB instruments This class extents the Instrument class with special operations and properties of GPIB instruments Parameters e gpib_identifier strings are interpreted as instrument s VISA resource name Numbers are interpreted as GPIB number board_number the number of the GPIB bus Further keyword arguments are passed to the constructor of class Instrument 3 4 API 41 PyVISA Documentation Release 1 5 stb Service request status register wait_for_srq timeout 25 Wait for a serial request SRQ coming from the instrument Note that this method is not ended when another instrument signals an SRQ only this instrument Parameters timeout the maximum waiting time in seconds Defaul 25 seconds None means waiting forever if necessary 3 4 2 Functions in the ctypes wrapper module pyvisa wrapper functions Defines VPP 4 3 2 wrapping functions adding signatures to the library This file is part of PyVISA copyright 2014 by PyVISA Authors see AUTHORS for more details license MIT see LICENSE for more details pyvisa ctwrapper funct
110. saLibrary All level 2 functions are bound methods of VisaLibrary Levels 1 and 2 are implemented in the same package called ctwrapper which stands for ctypes wrapper The higher level uses ctwrapper but in principle can use any package This will allow us to create other wrappers We have two wrappers planned e a Mock module that allows you to test a Py VISA program even if you do not have VISA installed e a CFFI based wrapper CFFI is new python package that allows easier and more robust wrapping of foreign libraries It might be part of Python in the future 2 6 Architecture 15 PyVISA Documentation Release 1 5 16 Chapter 2 User guide CHAPTER 3 More information 3 1 Migrating from PyVISA lt 1 5 You don t need to change anything in your code if you only use the instrument constructor and attributes and methods of the resulting object For example this code will run unchanged in modern versions of PyVISA import visa keithley visa instrument GPIB 12 print keithley ask x IDN This covers almost every single program that I have seen on the internet However if you use other parts of PyVISA or you are interested in the design decisions behind the new version you might want to read on Some of these decisions were inspired by the visalib package as a part of Lantz 3 1 1 Short summary PyVISA 1 5 has full compatibility with previous versions of PyVISA using the legacy module changing some
111. session e event_type Logical event identifier e handler Interpreted as a valid reference to a handler to be uninstalled by a client applica tion e user_handle A value specified by an application that can be used for identifying handlers uniquely in a session for an event pyvisa ctwrapper functions unlock library session Relinquishes a lock for the specified resource Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session pyvisa ctwrapper functions unmap_address library session Unmaps memory space previously mapped by map_address Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session 3 4 API 55 PyVISA Documentation Release 1 5 pyvisa ctwrapper functions unmap trigger library session trigger_source trig ger_destination Undo a previous map from the specified trigger source line to the specified destination line Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e trigger_source Source line used in previous map Constants TRIG e trigger_destination Destination line used in previous map Constants TRIG pyvisa ctwrapper functions usb_control_in library session request_type_bitmap_field re quest_id request_value index length 0 Performs a USB control pipe transfer from the device Par
112. sion event_type handler user_handle Installs handlers for event callbacks Parameters e library the visa library wrapped by ctypes session Unique logical identifier to a session event_type Logical event identifier handler Interpreted as a valid reference to a handler to be installed by a client application user_handle A value specified by an application that can be used for identifying handlers uniquely for an event type Returns a handler descriptor which consists of three elements handler a python callable user handle a ctypes object ctypes handler ctypes object wrapping handler pyvisa ctwrapper functions lock library session lock_type timeout requested_key None Establishes an access mode to the specified resources Parameters library the visa library wrapped by ctypes session Unique logical identifier to a session lock_type Specifies the type of lock requested either Constants EXCLUSIVE_LOCK or Constants SHARED_LOCK timeout Absolute time period in milliseconds that a resource waits to get unlocked by the locking session before returning an error requested_key This parameter is not used and should be set to VI_LNULL when lockType is VI EXCLUSIVE_LOCK Returns access_key that can then be passed to other sessions to share the lock pyvisa ctwrapper functions map_address library session map_space map_base map_size access 0 suggested 0
113. ssion before returning this operation with an error requested_key ctypes string optional This parameter is not used if lock_type is VI_EXCLUSIVE_LOCK exclusive locks When trying to lock the resource as VI_SHARED_LOCK shared you can either omit it so that VISA generates an access_key for the session or you can suggest an access_key to use for the shared lock Return values access_key ctypes string optional This value is None if lock_type is VI_EXCLUSIVE_LOCK exclusive locks When trying to lock the resource as VI_SHARED_LOCK shared the func tion returns a unique access key for the lock if the operation succeeds This access_key can then be passed to other sessions to share the lock map_address Map the specified memory space into the process s address space Call address map_address vi map_space map_base map_size access suggested VISA name viMapAddress Parameters vi integer Unique logical identifier to a session map_space integer Specifies the address space to map map_base ViBusAddress Offset in bytes of the memory to be mapped map_size integer Amount of memory to map in bytes access integer optional Must be VI_FALSE suggested integer optional If not VI_NULL the default the operating system attempts to map the memory to the address specified in suggested There is no guarantee however that the memory will be mapped to that address This operation may map the mem
114. t returns a list of decimal values floats sent from the instrument to the computer See section A more complex example above The list may contain only one element or may be empty The optional format argument overrides the setting of values_format For information about that see section Reading binary data Instrument ask message sends the string message to the instrument and returns the answer string from the instrument Instrument ask_for_values message format sends the string message to the instrument and reads the answer as a list of values just as read_values does The optional format argument overrides the setting of values_format For information about that see section Reading binary data 64 Chapter 4 Legacy Modules PyVISA Documentation Release 1 5 Instrument clear resets the device This operation is highly bus dependent I refer you to the original VISA documentation which explains how this is achieved for VXI GPIB serial etc Instrument trigger sends a trigger signal to the instrument Instrument read_raw returns a string sent from the instrument to the computer In contrast to read no termination characters are checked or stripped You get the pristine message Instrument timeout The timeout in seconds for each I O operation See section Timeouts for further information Instrument term_chars The termination characters for each read and write operation See section Term
115. the format specifier Store the formatted data in the given optional parameters Warning The current implementation only supports the following C data types Long double and char strings Thus you can only use these three data types in format strings for printf scanf and the like Call value1 value2 scanf vi read_format maximal_string_length 1024 VISA name viScanf Parameters vi integer Unique logical identifier to a session read_format string String describing the format for arguments integers floats or strings Arguments to be read from the device according to read_format It s totally insignificant which values they have they serve just as a cheap way to determine what types are to be expected So actually this argument list shouldn t be necessary but with the current implementation it is sorry These arguments may be however needn t be the same names used for storing the result values Alternatively you can give literals maximal_string_length integer keyword argument The maximal length assumed for string result arguments Note that string results must never exceed this length It defaults to 1024 4 3 Legacy API 85 PyVISA Documentation Release 1 5 Return values valuel value2 integers floats or strings Arguments read from the device according to read_format Of course this must be the same sequence as far as data types are concerned as the given argument
116. the same name as in the shared library and they are prefixed by vi Middle level functions have a friendlier more pythonic but still recognizable name 2 4 Advanced 9 PyVISA Documentation Release 1 5 2 5 Instruments class Instrument resource_namel keyw represents an instrument e g a measurement device It is independent of a particular bus system i e it may be a GPIB serial USB or whatever instrument However it is not possible to perform bus specific operations on instruments created by this class For this have a look at the specialised classes like GoibInstrument section Common properties of instrument variables The parameter resource_name takes the same syntax as resource specifiers in VISA Thus it begins with the bus system followed by continues with the location of the device within the bus system and ends with an optional INSTR Possible keyword arguments are Keyword Description timeout timeout in seconds for all device operations see section Timeouts Default 5 chunk_size Length of read data chunks in bytes see section Chunk length Default 20kB val Data format for lists of read values see section Reading binary data Default ascii ues_format term_char termination characters see section Termination characters Default None send_end whether to assert END after each write operation see section Termination characters Default True delay delay in seconds a
117. tion continues with the input stream immediately after the last termination sequence In PyVISA the termination characters are stripped off the message before it is given to you 12 Chapter 2 User guide PyVISA Documentation Release 1 5 You may set termination characters for each instrument e g my_instrument term_chars CR Alternatively you can give it when creating your instrument object my_instrument instrument GPIB 10 term chars CR The default value depends on the bus system Generally the sequence is empty in particular for GPIB For RS232 its CR oy Well the real default is not the empty string but None There is a subtle difference really means the termina tion characters are not used at all neither for read nor for write operations In contrast None means that every write operation is implicitly terminated with CR LF This works well with most instruments All CRs and LFs are stripped from the end of a read string no matter how term_chars is set The termination characters sequence is an ordinary string CR and LF are just string constants that allow readable access to W and WM Therefore instead of CR LF you can also write wn whichever you like more delay and send_end There are two further options related to message termination namely send_end and delay send_end is a boolean If it s True the default the EOI line is asserted after each write operatio
118. tions of the visa library move_out_16 library session space offset length data extended False Moves an 16 bit block of data from local memory to the specified address space and offset Parameters e library the visa library wrapped by ctypes session Unique logical identifier to a session space Specifies the address space Constants SPACE offset Offset in bytes of the address or register from which to read length Number of elements to transfer where the data width of the elements to transfer 1s identical to the source data width data Data to write to bus extended Use 64 bits offset independent of the platform Corresponds to viMoveOut16 functions of the visa library move_out_32 library session space offset length data extended False Moves an 32 bit block of data from local memory to the specified address space and offset Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session space Specifies the address space Constants SPACE offset Offset in bytes of the address or register from which to read length Number of elements to transfer where the data width of the elements to transfer is identical to the source data width data Data to write to bus extended Use 64 bits offset independent of the platform Corresponds to viMoveOut32 functions of the visa library move_out_8 libr
119. to 25 seconds Floating point values are allowed If you set it to zero all operations must succeed instantaneously You must not set it to None Instead if you want to remove the timeout just say del my_device timeout Now every operation of the resource takes as long as it takes even indefinitely if necessary The default timeout is 5 seconds but you can change it when creating the device object my_instrument instrument ASRL1 timeout 8 This creates the object variable my_instrument and sets its timeout to 8 seconds In this context a timeout value of None is allowed which removes the timeout for this device Note that your local VISA library may round up this value heavily I experienced this effect with my National Instru ments VISA implementation which rounds off to 0 1 3 and 10 seconds Chunk length If you read data from a device you must store it somewhere Unfortunately PyVISA must make space for the data before it starts reading which means that it must know how much data the device will send However it doesn t know a priori Therefore PyVISA reads from the device in chunks Each chunk is 20 kilobytes long by default If there s still data to be read PyVISA repeats the procedure and eventually concatenates the results and returns it to you Those 20 kilobytes are large enough so that mostly one read cycle is sufficient 2 5 Instruments 11 PyVISA Documentation Release 1 5 The whole thing ha
120. ts Note that string results must never exceed this length It defaults to 1024 Return values valuel value2 integers floats or strings Arguments read from the device according to read_format Of course this must be the same sequence as far as data types are concerned as the given argument list above status_description Return a user readable description of the status code passed to the operation Call description status_description vi status VISA name viStatusDesc Parameters vi integer ViEvent or ViFindList Unique logical identifier to a session status integer Status code to interpret Return values description string The user readable string interpretation of the status code passed to the opera tion 4 3 Legacy API 87 PyVISA Documentation Release 1 5 terminate Request a VISA session to terminate normal execution of an operation Call terminate vi degree job_id VISA name viTerminate Parameters vi integer Unique logical identifier to a session degree integer VI_NULL job_id ViJobld Specifies an operation identifier Return values None uninstall_handler Uninstall handlers for events Call uninstall_handler vi event_type handler user_handle VISA name viUninstallHandler Parameters vi integer Unique logical identifier to a session event_type integer Logical event identifier handler callable Interpreted as a valid reference to a handler to be uninstalled by a cli
121. ts created by this class For this have a look at the specialised classes like GoibInst rument section Common properties of instrument variables The parameter resource_name takes the same syntax as resource specifiers in VISA Thus it begins with the bus system followed by continues with the location of the device within the bus system and ends with an optional INSTR Possible keyword arguments are Keyword Description timeout timeout in seconds for all device operations see section Timeouts Default 5 chunk_size Length of read data chunks in bytes see section Chunk length Default 20kB val Data format for lists of read values see section Reading binary data Default ascii ues_format term_char termination characters see section Termination characters Default None send_end whether to assert END after each write operation see section Termination characters Default True delay delay in seconds after each write operation see section Termination characters Default O lock whether you want to have exclusive access to the device Default VI_NO_LOCK For further information about the locking mechanism see The VISA library implementation The class Instrument defines the following methods and attributes Instrument write message writes the string message to the instrument Instrument read returns a string sent from the instrument to the computer Instrument read_ values forma
122. ts software or hardware trigger Parameters e library the visa library wrapped by ctypes 42 Chapter 3 More information PyVISA Documentation Release 1 5 e session Unique logical identifier to a session e protocol Trigger protocol to use during assertion Constants PROT pyvisa ctwrapper functions assert_utility signal library session line Asserts or deasserts the specified utility bus signal Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e line specifies the utility bus signal to assert Constants UTIL_ASSERT pyvisa ctwrapper functions buffer_read library session count Reads data from device or interface through the use of a formatted I O read buffer Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e count Number of bytes to be read Returns data read Return type bytes pyvisa ctwrapper functions buffer_write library session data Writes data to a formatted I O write buffer synchronously Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e data bytes data to be written Returns number of written bytes pyvisa ctwrapper functions clear library session Clears a device Parameters e library the visa library wrapped by ctypes e session Unique logical identifi
123. ument Note that this method is not ended when another instrument signals an SRQ only this instrument The timeout argument given in seconds denotes the maximal waiting time The default value is 25 seconds If you pass None for the timeout this method waits forever if no SRQ arrives class Gpib board_number represents a GPIB board Although most setups have at most one GPIB interface card or USB GPIB device with board number 0 theoretically you may have more Be that as it may for board level operations i e operations that affect the whole bus with all connected devices you must create an instance of this class The optional GPIB board number board_number defaults to 0 4 3 Legacy API 65 PyVISA Documentation Release 1 5 The class Gp ib defines the following method Gpib send_ifc pulses the interface clear line IFC for at least 0 1 seconds Note You needn t store the board instance in a variable Instead you may send an IFC signal just by saying Gpib send_ifc Serial devices Please note that serial instrument means only RS232 and parallel port instruments i e everything attached to COM and LPT In particular it does not include USB instruments For USB you have to use Inst rument instead class SerialInstrument resource_namel keyw represents a serial instrument resource_name is the VISA resource name see section VISA resource names The general keyword arguments are inter
124. visa library wrapped by ctypes e session Unique logical identifier to a session in_16 library session space offset extended False Reads in an 16 bit value from the specified memory space and offset Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e space Specifies the address space Constants SPACE e offset Offset in bytes of the address or register from which to read e extended Use 64 bits offset independent of the platform Returns Data read from memory in_32 library session space offset extended False Reads in an 32 bit value from the specified memory space and offset Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e space Specifies the address space Constants SPACE e offset Offset in bytes of the address or register from which to read e extended Use 64 bits offset independent of the platform Returns Data read from memory in_8 library session space offset extended False Reads in an 8 bit value from the specified memory space and offset Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e space Specifies the address space Constants SPACE e offset Offset in bytes of the address or register from which to read e extended Use 64 bits offset independent of t
125. visarc must contain the following Paths VISA library usr lib libvisa so 7 Please note that Paths is treated case sensitively You can define a site wide configuration file at usr share pyvisa pyvisarc It may also be usr local depending on the location of your Python Under Windows this file is usually placed at c Python27 share pyvisa pyvisarc 2 4 Advanced You can mix the high level object oriented approach described in this document with middle and low level VISA function calls See Architecture for more information By doing so you have full control of your devices After you have instantiated the ResourceManager gt gt gt import visa gt gt gt rm visa ResourceManager you can access corresponding the VisaLibrary instance under the visalib attribute The VisaLibrary object contains low level functions as directly exposed by the foreign library for example gt gt gt rm visalib viMapAddress lt here goes the arguments gt To call this functions you need to know the function declaration and how to interface it to python To help you out the VisaLibrary object also contains middle level functions Each middle level function wraps one low level function In this case gt gt gt rm visalib map_address lt here goes the arguments gt The calling convention and types are handled by the wrapper You can recognize low an middle level functions by their names Low level functions carry
126. x integer Specifies the interface or endpoint index number depending on re quest_type_bitmap_field buffer string optional Actual data to send to the device during the Data stage If not given nothing is sent Return values None vprintf vqueryf vscanf vsprintf vsscanf These variants make no sense in Python so I realised them as mere aliases just drop the v vxi_command_query Send the device a miscellaneous command or query and or retrieve the response to a previous query Call vxi_command_query vi mode command VISA name viVxiCommandQuery Parameters vi integer Unique logical identifier to a session mode integer Specifies whether to issue a command and or retrieve a response command integer The miscellaneous command to send Return values response integer The response retrieved from the device If the mode specifies just sending a command this parameter may be VI_NULL wait_on_event Wait for an occurrence of the specified event for a given session Call out_event_type out_context wait_on_event vi in_event_type timeout VISA name viWaitOnEvent Parameters vi integer Unique logical identifier to a session in_event_type integer Logical identifier of the event s to wait for timeout integer Absolute time period in milliseconds that the resource shall wait for a specified event to occur before returning the time elapsed error Return values 90 Chapter 4 Legacy Modules PyVIS
127. xceptions with import warnings warnings filterwarnings error Consult the description of the warnings package for further information Name TypeError Description The current implementation of printf _ scanf _ sprintf _ sscanf _ and queryf _ have the limitation that only integers floats and strings are allowed as types for the arbitrary argu ments Additionally only format string directives for C longs C doubles and C strings are allowed to use albeit not checked However if you pass a list or a unicode string you get this exception The same exception is raised if an unsupported type is passed as user handle to install_handler _ See there for a list of supported types Name UnknownHandler Description Raised if an unknown handler user_handle pair is passed to uninstall_handler _ In par ticular you must save the user handle returned by install_handler _ in order to pass it to unin stall handler Moreover this module may pass exceptions generated by ctypes This may be because you ve passed a wrong type to a function or that the VISA library file was not found but it may also mean a bug in vpp43 itself So if you don t see why the exception was raised contact the current maintainers of PyVISA 4 3 Legacy API 4 3 1 legacy visa functions get_instruments_list use_aliases returns a list with all instruments that are known to the local VISA system If you re lucky these ar
128. y wrapped by ctypes session Unique logical identifier to a session map_space Specifies the address space to map Constants SPACE map_base Offset in bytes of the memory to be mapped map_size Amount of memory to map in bytes access suggested If not Constants NULL 0 the operating system attempts to map the memory to the address specified in suggested There is no guarantee however that the memory will be mapped to that address This operation may map the memory into an address region different from suggested Returns Address in your process space where the memory was mapped map_trigger library session trigger_source trigger_destination mode Map the specified trigger source line to the specified destination line Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e trigger_source Source line from which to map Constants TRIG e trigger_destination Destination line to which to map Constants TRIG 28 Chapter 3 More information PyVISA Documentation Release 1 5 e mode memory_allocation library session size extended False Allocates memory from a resource s memory region Parameters e library the visa library wrapped by ctypes e session Unique logical identifier to a session e size Specifies the size of the allocation e extended Use 64 bits offset independent
129. ython is rather different from C and Visual Basic most notably because of lacking call by reference The second important difference are strings In C they are null terminated whereas Python doesn t have this constraint The slightly odd name vpp43 for this module derives from the necessity to make name space for the visa module that is supposed to realise the actual high level VISA access in Python The VXIplug amp play Systems Alliance used to maintain the VISA specifications and although today the IVI foundation is responsible for this task the files are still called vpp43 doc etc So I thought vpp43 was an appropriate name You may wonder why I did choose new names for all routines I did so because Python has its own naming guidelines and because it shows that the routines had to be adapted However I didn t change them really Every routine is a 1 1 counterpart By calling them from C you could even create a C based VISA implementation with the original function signatures and semantics Moreover the new names are mere expansions of the original ones 4 2 1 Connecting to the VISA shared object vpp43 tries to find the VISA library for itself On Windows this is not a big problem visa32 d11 must be in your PATH If it isn t move it there or expand your PATH However on Linux you may need to give the explicit path to the shared object file You do so by saying for example from pyvisa legacy import vpp43 vpp43 visa_library load_

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