SM1 Protocol Converter User Manual Instrumental Solutions, Inc.
Contents
1. 1 SDI12 data line 2 SDI12 ground 3 12VDC input to SM1 and SDI 12 device 4 Ground 5 Transmit data RS232 output same as DB9P pin 3 6 Receive data RS232 input same as DB9P pin 2 7 RS485 line A 8 RS485 line B Default Configuration To view the current configuration or configure the SM1 it is first necessary to move the jumper on header J6 which is located immediately behind the screw terminal block from its normal 2 3 position to position 1 2 This jumper must be returned to position 2 3 for the ModBus interface to work Please refer to the highlighted portion in Figure 1 where the jumper is shown in position 2 3 Next plug one end of a null modem cable as described above into the DB9P connector on the converter and the other end into an available serial port on a PC Terminal software should be set for 9600 baud 8 data bits no parity and no flow control To enter configuration mode quickly type 3 question mark characters The SM1 should respond with the following screen Copyright 2009 Instrumental Solutions Inc All Rights Reserved 4 serial HyperTerminal File Edit View Call Transfer Help 3 0 0 ISI SM1 SDI12 Modbus Converter Firmware v1 1 ISOS 11 kernel v2 0 Copyright 2008 Instrumental Solutions Inc SDI12 address 0 Concurrent measurement No Use CRC Yes Modbus address Restore default settings Resume normal oper2. SM1 Protocol Converter User Manual st CP PAT eee EL LES SDI 12 ModBus Protocol Converter ModBus SDI 12 S ER ZEN ISI Instrumental Solutions Inc WWW ISIDEV NET Introduction The SM1 protocol converter can take readings from an SDI 12 instrument and make the data available on a ModBus network On the SDI 12 side concurrent amp non concurrent measurements are supported as well as measurements using CRC error detection The SM1 can be configured to use any SDI 12 address from 0 9 On the ModBus side the SM1 address is configurable from 1 247 ModBus ASCII protocol is supported at 9600 baud 8 data bits no parity The electrical interface is standard RS 485 For more information on the ModBus interface see the ModBus Registers section The unit is configurable via a text based user interface using most any terminal software Getting Started All wiring connections are made inside the weatherproof enclosure with the wires passing through the waterproof fitting on the rear panel of the enclosure Remove the rear panel by removing the 4 retaining screws and slide the circuit board out to gain access to the connectors see Figure 1 The DB9P connector is used for configuring the SM1 A null modem serial cable with a female DB9 on each end is used to connect the unit to a PC serial port The cable only needs to have pins 2 3 amp 5 wired with pins 2 amp 3 swapped from end to end Any s
3. ace Modbus interface Text interface Operating system Indicators Connections Temperature range Power requirements Enclosure External dimensions Weight O Copyright 2009 Instrumental Solutions Inc All Rights Reserved SDI 12 v1 3 compliant Modbus ASCII 9600 baud 8 bit no parity 9600 baud 8 bit no parity no handshake Instrumental Solutions ISOS 11 2 bicolor LEDs for transmit receive indication Internal screw terminals DB9 male DTE 40 C to 85 C 12VDC 35ma idle 35 ma avg 55ma max Extruded aluminum IP65 rated 7 52 19 1cm L 3 48 8 84cm W 1 85 4 7cm H 15 ounces 10
4. ation Connected 0 00 22 ANSI 9600 8 N 1 NOTE If the converter fails to respond try again typing as quickly as you can If still no response remove and re apply power to the converter while watching the front panel LEDs Both LEDs should immediately light up red then turn green after about half a second then go out after another half second If this doesn t happen check the power wiring for proper voltage and polarity The SM1 operates on 9 14 volts DC If the LEDs don t light when power is applied there is a problem with the converter If the LEDs light but there is still no response after typing question marks make sure that you are using a null modem serial cable wired as described above in the Getting Started section If the unit fails to respond there may be a problem with the converter The default configuration is as follows SDI12 address 0 Concurrent measurement no Use CRC yes Modbus address 1 Copyright 2009 Instrumental Solutions Inc All Rights Reserved 5 To change a configuration setting type the number of the setting followed by the Enter key The configuration mode has an inactivity timeout of 1 minute If at any point during configuration the user goes 1 minute without typing anything the converter automatically returns to normal online operation Setting changes are saved as they are entered so any changes completed during the configuration session will not be lost if a inactivity timeout o
5. ccurs The following section describes each setting in detail 1 SDI12 address This is the address that the SM1 will use when communicating with the SDI 12 instrument The default value is 0 This value must match the address of the SDI 12 instrument 2 Concurrent measurement This setting determines the type of SDI 12 measurement request that is issued to the SDI 12 instrument If concurrent measurement is turned off the SM1 will issue the SDI 12 Start Measurement command M If turned on the Start Concurrent Measurement command C will be used The data acquisition cycle is usually faster when using the Start Measurement non concurrent command The default is to use non concurrent measurements 3 Use CRC This setting determines whether or not the SM1 requests a CRC cyclic redundancy check when issuing a measurement request CRC is used to detect errors caused by line interference in the data received by the SM1 If an error is detected the SM1 will re request the data The default is to use CRC 4 Modbus address This is the address that the SM1 will respond to on the ModBus interface The default value is 1 This value must match the address that the ModBus master uses when communicating with the SM1 5 Restore default settings This selection resets all configuration parameters to the factory default settings Copyright 2009 Instrumental Solutions Inc All Rights Reserved 6 6 Resume normal opera
6. er 1 the data portion of the ModBus response from the SM1 will be the following 20 bytes in hexadecimal 0031 0032 0033 002e 0034 0035 0000 0000 0000 0000 The data is shown in 16 bit groups to reflect each of the 10 Unicode characters returned by the SM1 The least significant byte of each Unicode character contains the ASCII code for the data value 31 1 Copyright 2009 Instrumental Solutions Inc All Rights Reserved 7 32 2 33 3 2e 34 4 35 5 00 NULL terminator 00 NULL pad character 00 NULL pad character 00 NULL pad character ModBus Function Codes The ModBus master uses Function Codes to tell the ModBus slaves what type of operation to perform Read Holding Register Write Holding Register etc These are simple 1 character values that identify each ModBus command The SM1 supports the following Function Codes the character value of the function code is also shown Read Holding Registers 0x03 Write Holding Register 0x06 To read a data holding register on the SM1 the ModBus master must use the Read Holding Registers function code The SM1 uses the Write Holding Register function code to initiate a measurement on the SDI 12 instrument The following section describes how this works Initiating a Measurement The data holding registers on the SM1 will contain zeroes until it takes a measurement on the SDI 12 device After that they will con
7. erial terminal program such as Hyperterm can be used See Table 1 for more information on the DB9P connections The SDI 12 instrument connects to the screw terminal block using terminals 1 3 labeled SDI12 GND and 12V respectively See Table 2 for more information on the terminal block connections Note that terminal 3 which is used to supply 12 volts to the SM1 can also be used to power the SDI 12 instrument The converter has 2 bi color LED indicators on the front panel for indicating SDI12 and Modbus data activity The indicators light up green when the converter is receiving data on the associated interface and red when the converter is sending data on the interface These can be used to help diagnose communication problems Copyright 2009 Instrumental Solutions Inc All Rights Reserved 2 w 0 n oe SHC11 Carr C 2008 4 Copyright 2009 Instrumental Solutions Inc All Rights Reserved Table 1 DB9P Connections Pin 1 No connection Pin 2 Receive data RS232 input Pin 3 Transmit data RS232 output Pin 4 DTR internally tied to pin 6 for flow control loopback Pin 5 Signal ground Pin 6 DSR internally tied to pin 4 for flow control loopback Pin 7 RTS internally tied to pin 8 for flow control loopback Pin 8 CTS internally tied to pin 7 for flow control loopback Pin 9 No connection Table 2 Terminal Connections
8. tain the data from the last SDI 12 measurement taken The data holding registers can be read at any time and reading them does not have any affect on their value A complete data acquisition cycle involves first telling the SM1 to take a reading from the SDI 12 device waiting for the reading to complete then reading the data holding register s to get the results Copyright 2009 Instrumental Solutions Inc All Rights Reserved 8 The SM1 has a status register at register address 1000 that is used to initiate measurements and indicate when a measurement has completed This register is just like the data holding registers except that it can be written to in addition to being read This register normally contains zero To initiate a measurement the ModBus master must use the Write Holding Register function code to write a value of to the register This starts the measurement process on the SDI 12 side The ModBus master should then read the status register using the Read Holding Registers function code repeatedly until the returned value is zero which indicates that the measurement is complete A polling rate of once a second is sufficient when reading the status register As soon as the status register goes to zero the ModBus master may then read 1 or more data holding registers registers 1 20 to retrieve the SDI 12 data Copyright 2009 Instrumental Solutions Inc All Rights Reserved 9 Specifications SDI 12 interf
9. tion This selection exits configuration mode and returns the converter to online operation Configuration mode has an inactivity timeout of 1 minute if at any time after entering configuration mode no characters are typed for 1 minute the converter will automatically return to normal online operation ModBus Registers Each data field from the SDI 12 instrument is available in an individual data holding register on the SM1 The maximum number of data fields supported is 20 and the data holding registers are numbered 1 20 Data fields received from the SDI 12 device are placed in the data holding registers starting with register 1 in the order they are received from the SDI 12 device Each numbered data holding register in the SM1 1 2 3 etc is 10 registers wide internally allowing for the storage of 20 characters of data a ModBus register is 2 characters or bytes in size As a result the ModBus master should use a register count of 10 when reading a data holding register on the SM1 which will result in 10 registers of data being returned by the SM1 Each of the 10 registers returned contains 1 Unicode character On the SM1 a Unicode character has an ASCII character code in the least significant byte LSB and a zero in the most significant byte MSB For example let s say the first field returned by the SDI 12 instrument is the value 123 45 When the ModBus master issues a Read Holding Register command to read register numb
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