M930 Modbus
Contents
1. an RTU since each byte needs two characters The format 10 bits for each byte in ASCII mode is Coding System Hexadecimal ASCII characters 0 9 A F One hexadecimal character contains 4 bits of data within each ASCII character of the message Bits per Byte 1 start bit 7 data bits least significant bit sent first 1 bit for parity completion 1 stop bit The default parity mode is Even parity Remark the use of no parity requires 2 stop bits ASCII Message framing 1 char 2 chars 2 chars 0 up to 2x252 char s 2 chars 2 chars CR LF In ASCII mode a message is delimited by specific characters as Start of frames and End of frames A message must start with a colon character ASCII 3A hex and end with a carriage return line feed CRLF pair ASCII 0D and 0A hex In ASCII mode messages include an error checking field that is based on a Longitudinal Redundancy Checking LRC calculation that is performed on the message contents exclusive of the beginning colon and terminating CRLF pair characters 1 2 2 RTU mode When devices communicate on a MODBUS serial line using the RTU Remote Terminal Unit mode each 8 bit byte in a message contains two 4 bit hexadecimal characters The main advantage of this mode is that its greater character density allows better data throughput than ASCII mode for the same baud rate Each message must be transmitted in a continuous stream of character2. and negative volume clear bit R W CLRVM 0x1006 Direct reset from Main menu bit R W FME Bit variables data format ON is expressed as 0xff00 OFF is expressed as 0x0000 3 2 Table 2 Integer variables holding registers Address Name Type Access RS232 command 0x3000 Nominal diameter integer R W RDN 0x3002 Datalogger filling bytes integer R DBT Integer variables data format MSB LSB most sign bit least sign bit IXIXIXIXIXIXIXIXI IXIXIXIXIXIXIXIXI amp Operation manual MODBUS protocol MEATEST spol s r o 3 3 Table 3 Long variables holding registers Address Name Type Access RS232 command 0x5000 Calibration password access setting long R W FPC 0x5002 Password setting long W PSW 0x5004 Basic password access setting long R W FPB 0x5006 Errors reading long R IER 0x5008 Datalogger number of samples long R DNR Long variables data format MSB LSB most sign bit least sign bit IXIXIXIXIXIXIXIXI IXIXIXIXIXIXIXIXI IXIXIXIXIXIXIXIX IXIXIXIXIXIXIXIXI byte 3 byte 2 byte 1 byte 0 Table 5 Char variables holding registers Address Name Type Access RS232 command 0x6001 Flowrate unit char R W FFS 0x6002 Volume unit char R W FVS 0x6003 Time constant char R W FTC 0x6004 Excitation frequency char R W FEC 0x6005 Datalogger step char R W DST 0x6007 Language se
3. MODBUS M930 protocol description User s manual MODBUS protocol MEATEST spol s r o CONTENT 1 BASIC INFORMATION 4 1 1 INTRODUCTION TO MODBUS 4 1 2 TRANSMISSION FORMAT 4 1 2 1 ASCII MODE 4 1 2 2 RTU MODE 5 2 SUPPORTED FUNCTIONS 7 2 1 READ COIL STATUS FUNCTION 01 7 2 2 READ INPUT STATUS FUNCTION 02 7 2 3 READ MULTIPLE HOLDING REGISTERS FUNCTION 03 7 2 4 READ INPUT REGISTERS FUNCTION 04 7 2 5 WRITE SINGLE COIL FUNCTION 05 7 2 6 WRITE MULTIPLE HOLDING REGISTERS FUNCTION 16 7 3 COMMANDS TABLE 3 1 TABLE 1 BIT VARIABLES SINGLE COILS 8 3 2 TABLE 2 INTEGER VARIABLES HOLDING REGISTERS 8 3 3 TABLE 3 LONG VARIABLES HOLDING REGISTERS 9 3 4 TABLE 4 TIME LONG VARIABLES HOLDING REGISTERS CHYBA ZALOZKA NENI DEFINOVANA 3 5 TABLE 5 CHAR VARIABLES HOLDING REGISTERS 9 3 6 TABLE 6 FLOAT VARIABLES HOLDING REGISTERS 9 3 7 TABLE 7 STRING VARIABLES HOLDING REGISTERS 11 3 8 TABLE 8 DOUBLE VARIABLES HOLDING REGISTERS 11 Operation manual version 10 3 MEATEST spol s r o MODBUS protocol 1 Basic information 1 1 Introduction to Modbus This document specifies the MODBUS communications protocol as implemented on the magnetic flowmeter M930 This manual does not try to be a complete guide to the MODBUS protocol but will show how to structure a message that the instruments will recognize For Modbus communication is used USB interface Instruments communicate using a master slave tech
4. e read only one variable using this function 2 4 Read input registers Function 04 Function 3 and 4 perform the same action see description of Function 03 2 5 Write single coil Function 05 Function writes to a single coil value ON or OFF ON value is presented as Oxff00 OFF value is presented as 0x0000 Command contains the coil address and reguested value The normal response is an echo of the command returned after the coil state has been changed 2 6 Write multiple holding registers Function 16 Function writes new values into a segunce of holding registers Command contains the register starting address number of affected registers and reguested values The normal response contains number of changed registers In this function can be write just one variable integer float double Operation manual 7 MEATEST spol s r o MODBUS protocol 3 Commands table Tables in this chapter contain following columns description of variables 1 Address 2 Name 3 Type 4 Access Read Write 5 RS232 command see description of this command in the user s manual 3 1 Table 1 Bit variables single coils Address Name Type Access RS232 command 0x1000 Negative flow direction bit R W FFD Ox1001 System error status bit R RES 0x1002 Auxiliary volume clear bit R W CLRAV 0x1003 Total volume clear bit R W CLRVO 0x1004 Datalogger clear bit R W DCLR 0x1005 Positive
5. nigue in which only one device is the master and theslave devices supply the reguested data when addressed Typical master devices can be a host computer Only the master can initiate transactions reguests and only the addressed device responds The Modbus reguest consist of an address e a function code defining the requested action data if necessary for the requested function and error check for testing the integrity of the message The slave s response contains e the slave address data conform the request type and error check If the data integrity test fails no response is sent back If a request cannot be processed an exception message is returned 1 2 Transmission format There are two serial transmission modes for the MODBUS protocol ASCII or RTU Remote Transmission Unit framing The user has to select the desired protocol along with the serial communication parameters baud rate paritytype Note that all these parameters must be the same for all instruments in the network 1 2 1 ASCH mode When device communicate on a MODBUS serial line using ASCII mode each 8 bit byte in a message is sent as two ASCII characters This mode is used when the physical communication link or the capabilities of the device does not allow the conformance with RTU mode requirements regarding timers management Remark this mode is less efficient th 4 Operation manual MODBUS protocol MEATEST spol s r o
6. rmat MSB most sign bit S E E E E E E E E EJE EIMIMIMIM IMIMIMIMIMIMIMIMI IMIMIMIMIMIMIMIMI LSB IMIMIMIMIMIMIMIMI IMIMIMIMIMIMIMIMI IMIMIMIMIMIMIMIMI IMIMIMIMIMIMIMIMI Where S sign bit where 1 is negative and 0 is positive E exponent with an offset of 1023 M 53 bit mantissa stored in 52 bits The mantissa is a 53 bit value whose most significant bit MSB is always 1 and is therefore not stored Operation manual 11
7. s The format 11 bits for each byte in RTU mode is Coding System 8 bit binary Bits per Byte 1 start bit 8 data bits least significant bit sent first 1 bit for parity completion 1 stop bit The default parity mode is even parity Operation manual 5 MEATEST spol s r o MODBUS protocol Remark the use of no parity requires 2 stop bits RTU Message framing gt 3 5 char 1 byt 1 byt 0 up to 252 byte s 2 bytes gt 3 5 char In RTU mode message frames are separated by a silent interval of at least 3 5 character times The RTU mode includes an error checking field that is based on a Cyclical Redundancy Checking CRC method performed on the message contents 6 Operation manual MODBUS protocol MEATEST spol s r o 2 Supported functions 2 1 Read coil status Function 01 Function reads the ON OFF status of discrete inputs or discrete bit variables in the instrument Query contains the starting coil address and the guantity of coils to be read 2 2 Read input status Function 02 Function 1 and 2 perform the same action see description of Function 01 2 3 Read multiple holding registers Function 03 Function reads the binary contents of holding registers in the instrument Ouery contains the starting registr address and the guantity of registers to be read The maximum number of registers at each reguest is limited to 44 RTU or 22 ASCII Exception is double which can b
8. tage 5V float R IU3 0x7022 Internal voltage 3 6V float R IU4 0x7024 Internal voltage 3 6V float R IUS 0x7026 Reference voltage 2 5V float R IU6 0x7028 Excitation coils current float R ICO 0x602A Datalogger filling percentage float R DPC Float variables data format MSB LSB most sign bit least sign bit IS E E E E E EJE E MIMIMIMIMIMIM IMIMIMIMIMIMIMIMI IMIMIMIMIMIMIMIMI Where S sign bit where 1 is negative and 0 is positive E exponent with an offset of 127 M 24 bit mantissa stored in 23 bits The mantissa is a 24 bit value whose most significant bit MSB is always 1 and is therefore not stored 10 Operation manual MODBUS protocol MEATEST spol s r o 3 5 Table 7 String variables holding registers Address Name Type Access RS232 command 0x8000 Device identification string 22 R IDN 0x800B Flowrate unit user text string 6 R W FFU Ox800E Volume unit user text string 4 R W FVU String variables data format String variables have defined length see table above and consists of ASCII characters One byte represents one character 3 6 Table 8 Double variables holding registers Address Name Type Access RS232 command 0x9000 Volume double R RVO 0x9004 Volume positive double R RVP 0x9008 Volume negative double R RVN 0x900c Volume auxiliary double R RVA Double variables data format decimal 64 data fo
9. tting char R W FLG 0x6008 Number of calibration points char R W CPN 0x6009 Contrast setting char R W FDC 0x600a Message time setting char R W FDM 0x600b Date format setting char R W FDF 0x600c Actual access level char R W PAL Char variables data format MSB most s bit LSB least s bit 3 4 Table 6 Float variables holding registers Operation manual MEATEST spol s r o MODBUS protocol Address Name Type Access RS232 command 0x7000 Conversion constant for flowrate user float R W FFC unit 0x7002 Conversion constant for volume user float R W FVC unit 0x7004 Low flow cutoff float R W FLF 0x7006 Actual flowrate float R RFL 0x7008 Nominal flowrate float R W RQN 0x700a Electroni unit temperature float R IT 0x700c Nominal value of calibration point 1 float R W CXI 0x700e Calibration constant for calibration float R W CY1 point 1 0x7010 Nominal value of calibration point 2 float R W CX2 0x7012 Calibration constant for calibration float R W CY2 point 2 0x7014 Nominal value of calibration point 3 float R W CX3 0x7016 Calibration constant for calibration float R W CY3 point 3 0x7018 Nominal value of calibration point 4 float R W CX4 Ox701a Calibration constant for calibration float R W CY4 point 4 0x701c Battery voltage float R IU1 0x70le CPU voltage float R IU2 0x7020 Internal vol
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