MQU & MHU Modbus User Guide, ENG 23-03-2011
Contents
1. protocol v 1 Using Modbus RTU RS485 module at Modbus RTU mode For this standard using Modbus RTU RS485 module this module must be configured for Modbus protocol without corresponding jumper Furthermore MQU99 or flowmeter with Modbus RTU RS485 module at Modbus RTU mode must have the following communication parameters equal to factory settings Device address 31 Baud rate 9600 Bd R T timeout 10 0 ms These parameters are available by means of the flowmeter local keyboard and display MAIN menu RS 485 offer e Modbus RTU RS485 module and SmartMQU software SmartMQU data acquisition software can communicate in ELA 1 protocol only Therefore while using this software with MQU99 flowmeter equipped by Modbus RTU RS485 module this module must be configured for ELA protocol with corresponding jumper Modbus RTU Module User Guide 9 V1 3 29 04 2011 7 CONTACT Technical support support arkon co uk Windows life messenger support Darkon co uk Sales office office arkon co uk Office hours 8 30 18 00 GMT 1 Direct technical support 8 00 16 30 GMT 1 Modbus RTU Module User Guide 10 V1 3 29 04 20112. 2 V1 3 29 04 2011 1 INTRODUCTION This manual describes the Modbus RTU communication protocol 1 1 Definitions and Abbreviations CRC Cyclic Redundancy Check Used for error checking in Modbus RTU See appendix Modbus master A Modbus device which is able to access data in one or more connected Modbus slaves Modbus slave A Modbus device which is able to respond to requests from a single Modbus master Modbus address Throughout this document the following notation is used to address Modbus RTU registers e 1234 Holding register e 1234 addressed in messages by 1233 RS 232 Refers to the communication standard defined by EIA TIA 232C Physical layer EIA TIA232C USB Refers to the USB Specification usb org RS 485 Refers to the 2 wire communication standard defined by EIA TIA 485 Physical layer RTU Remote Terminal Unit Standard Modbus transmission mode 1 2 References Reference 1 Modbus over Serial Line Specification amp Implementation guide v 1 0 Modbus org 12 02 02 Reference 2 Modbus Application Protocol Specification v 1 1 Modbus org 12 06 02 Reference 3 MQU manual Modbus RTU Module User Guide 3 V1 3 29 04 2011 2 TECHNICAL DATA Modbus RTU specification Device type Slave Baud rates Recommended 4800 9600 14400 19200 38400 56000 57600 115200 bits sec Device address range max 31 per segm
3. 6 105 4 Long 0 Bo te RAW Device RT 108 107 4 Long 0 70 Timeout R W ms Device RT 110 109 4 Long 0 70 Mes RAW ms 112 114 4 Long 0 255 Device info R W 1 0 1 Bool 0 1 Relay 1 R 2 1 1 Bool 0 1 Relay 2 R 3 2 1 Bool 0 1 Relay 3 R 4 3 1 Bool 0 1 Relay 4 R 4800 9600 14400 19200 38400 56000 57600 115200 If you write the wrong value to the Baudrate item the default value 9600 will be written to this item Parity values 0 None 1 stopbit Modbus RTU Module User Guide V1 3 29 04 2011 When writing to the Holding registers data validity is not checked Writing incorrect values can result in unexpected behaviour of the device In any further explanations the following data types are used Longint Number consisting of 32 bits formed by 2 Modbus registers It is necessary to write both Low and High Words of this item the register number always has to be an even number Not meeting these requirements will cause an Exception 2 error illegal data address In case information about the number of decimals is available then the final number is given by the following formula Y X 10 DEC where Y is the final number X the read number and DEC the number of decimals Bool this item can be read but its value has no meaning Writing value 1 to this item will cause an unspecified operation to be performed erasing the Memory module resetting the flow totali
4. ar arkon fo MQU amp MHU L flow systems Arkon Flow Systems 19 Prizova 1 3 602 00 Brno Czech Republic Tel 420 543 214 822 Tel Fax 420 543 215 249 Enquiries Orders General questions office Darkon co uk Marketing support Brochures marketing arkon co uk Technical support support arkon co uk www arkon co uk List of Contents 1 INTRODUCTION veisiscccescccsccscecssccescseectcinssecescosescecdeoncecesosescascebsecseansoeessceceoscosseoscseestunceecedseosteosssscecoaseoees 3 1 1 Definitions and abbreviatiONS cocoocccccononnnnnnnnnononononononononononononononononononononononononononononononnnonononononononononononononononos 3 SAS A A RD ER tr a DS a tt re tisse rte eee et 3 2 TECHNICAL MENA O 4 2 1 General Modbus RTU 4 2 Rare BEER aaa tree 4 3 COMMISSIONING 5 22 82 e ner deco nt Cimo Cai d lentes Dole an te med 0 dada sil oe Reais assess des 5 4 Modbus ADDRESSING MODULE ccccssssssssssssssssssscecsccsccsesssscesscccccessssscsesececcscssssscsscecscccessssscsceees 6 4 Modbus TUCASA entente de rires 6 5 Modbus HOLDING REGISTERS sacccescccscssecsccscosccssesesccscccsassessocsesccecsssodsesscocseccescscoces nenne sans 7 6 Modbus RS485 MODULE FOR MQU 99 zussseesssssseessnnssessnssssssensnsssesssnnssesssnnnssnenssnssnenssnsssesssnssssnee 9 FICONTA Css nn E nan ed een tn ss also dar te fi ts ee a esse nee ce 10 Modbus RTU Module User Guide 1 V1 3 29 04 2011 Modbus RTU Module User Guide
5. ata register blocks Holding registers Le the module will not support the other standard data register blocks e Coils e Discrete input Input registers 4 1 Modbus function codes This device supports the following function codes 3 16 and 17 Function code 3 and 16 are used for accessing registers Function code 17 report slave ID will return a structure of identification information of the device Below the different function code exceptions are described Function code 3 Read holding registers General exceptions Requesting less than 1 or more than 125 registers gt Exception 3 illegal data value Requesting more than max message size gt Exception 2 illegal data address e Requesting data above crossing limitation of max register address OxFFFF gt Exception 2 illegal data address If the end address is only part of a mapped holding register item e g one half of a longint value gt Exception 2 Illegal data address Application exceptions Application errors gt Exception 2 illegal data address Holes register alignment The read command always returns data if no exception is given Bad start end alignment will result in only parts of the data item being read Holes in the holding register map return Exception 2 illegal data address Function code 16 Write multiple registers General exceptions Exceeding max message size gt Exception 2 illegal data addre
6. d responses Slave address Function code Data CRC 1 Byte 1 Byte 0 252 Bytes 2 Bytes Further details of the Modbus protocol can be found in Reference 1 and 2 Modbus RTU Module User Guide 4 V1 3 29 04 2011 3 COMMISSIONING Before communicating with the master Baud rate node ID and update rate must be selected This can be done from the display Please look in to the MQI MQU transmitter manual to locate the Modbus RTU menu see Reference 3 38400 115200 56000 57600 Item Value Comments Slave address 1 247 Device address Factory setting 1 Baud rate 4800 9600 14400 19200 Communication speed Factory setting 9600 Parity framing Even 1 stopbit Odd 1 stopbit None 2 stopbit None 1 stopbit Communication parameters Factory setting Even 1 stopbit Response delay 0 255 msec The minimum time from when a slave receives a request and until it returns a response This makes it possible to send data to slow masters without overwhelming its receiver Factory setting 0 Interframe 3 5 25 chars The minimum interframe space between two Modbus RTU spacing messages in sequence specified as 3 5 characters is configurable Range 3 5 25 character times Factory setting 3 5 Modbus RTU Module User Guide 5 V1 3 29 04 2011 4 Modbus ADDRESSING MODULE The module allows R W access to the following standard Modbus d
7. ent without repeaters Number of stations 1 247 Protocol Modbus RTU Other Modbus protocols like ASCII Plus or TCP IP are not supported Electrical interface RS232 RS 485 2 wire USB Ethernet Supported function code e 3read holding registers e 16 write multiple registers Broadcast No Maximum cable length Reference 3 Standard Modbus over serial line v1 0 Certified No 2 1 General Modbus RTU The module complies with the Modbus serial line protocol Reference 1 Among other things this implies a masterslave protocol at level 2 of the OSI model One node the master issues explicit commands to one of the slave nodes and processes responses Slave nodes will not transmit data without a request from the master node and do not communicate with other slaves Modbus is a mono master system which means that only one master can be connected at any single point in time Two modes of communication are possible Unicast and Broadcast Unicast mode is where the master sends a request to one slave device and waits a specified time for a response In Broadcast mode the master sends out a request to address 0 which means that the information is for all slave devices on the network In Broadcast mode there is no response from the slave devices UNICAST MODE Master BROADCAST MODE The Modbus frame is shown below and is valid for both requests an
8. sers etc Reference 3 It is necessary to write both Low and High Words of this item the register number always has to be an even number Not meeting these requirements will cause an Exception 2 error illegal data address Floating point values are represented in standard IEEE format Size of floating point value is 32 bits Range represented number is from 1 18E 38 up to 3 39E 38 Sign bit bit31 the most significant bit represents the sign of the number 0 for positive 1 for negative Exponent bits bits 30 23 the next 8 bits represent the exponent Mantissa bits bits 22 0 the remaining 23 bits represent the mantissa Data type memory map Modbus register Data Type Low High Word Longint Longint Bool Bool Floating point Tri TIC Floating point Word III A BB Ww ND Modbus RTU Module User Guide 8 V1 3 29 04 2011 6 Modbus RS485 MODULE FOR MQU99 MQU99 communication modules and protocols overview MQU99 ultrasonic flowmeters can be equipped with the following communication modules e RS232C module with company protocol e RS485 module with company protocol e Modbus RTU RS485 module with Modbus and company protocols Ag Selection between these protocols is done by means of a module on board jumper Modbus without jumper company protocol with jumper Note about company protocol versions MQU99 ultrasonic flowmeters have company
9. ss e Writing data above crossing limitation of max register address OxFFFF gt Exception 2 illegal data address Application exceptions Application errors gt Exception 2 illegal data address Application errors include writing to ReadOnly holding registers Holes register alignment If start address is not the start of a mapped holding register gt Exception 2 illegal data address e Writing to holes is not allowed gt Exception 2 illegal data address If the end address is only part of a mapped holding register item e g one half of a longint value the action depends on the data type If the end address is only part of a mapped holding register item e g one half of a longint value gt Exception 2 illegal data address Modbus RTU Module User Guide 6 V1 3 29 04 2011 5 Modbus HOLDING REGISTERS In the following the holding registers for the MQU 99 Modbus RTU module are described an de dl Ss mn Data type Min Value Max Value Pe bie a 1000 999 4 Float HA m R 1002 1001 4 Float HB m R 1004 1003 4 Float Qa m hr R 1006 1005 4 Float Qb m hr R 1008 1007 4 Float Fail R 1010 1009 4 Float Sa m R 1012 1011 4 Float Sb m R 1014 1013 4 Float Ta h R 1016 1015 4 Float Tb h R Modbus 100 99 4 Long 4800 115200 Baud Rate R W 102 101 4 Long 0 3 Parity R W 104 103 4 Long 1 247 ns RAW 10
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