Instruction manual

6. MODBUS COMMUNICATION PROTOCOL

IMR01H02-E3

6.2 Function Code

Function code contents

Function code

(Hexadecimal)

Function Contents

03H Read holding registers Measured value (PV), alarm status, etc.

06H Preset single register Set value (SV), alarm set value, PID constants,

PV bias, etc. (For each word)

08H Diagnostics (loopback test) Diagnostics (loopback test)

10H Preset multiple registers Set value (SV), alarm set value, PID constants,

PV bias, etc.

Message length of each function (Unit: byte)

Function code Function Query message Response message

(Hexadecimal) Min Max Min Max

03H Read holding registers 8 8 7 255

06H Preset single register 8 8 8 8

08H Diagnostics (loopback test) 8 8 8 8

10H Preset multiple registers 11 255 8 8

6.3 Communication Mode

Signal transmission between the master and slaves is conducted in Remote Terminal Unit (RTU)

mode.

RTU mode

Items Contents

Data bit length 8 bit (Binary)

Start mark of message Unused

End mark of message Unused

Message length See 6.2 Function Code

Data time interval 24 bit’s time or less *

Error check CRC-16 (Cyclic Redundancy Check)

* The data time intervals in one query message from the master must be 24 bit’s time or less. If the

data time interval exceeds 24 bit’s time, the slave regards the transmission as ended and because the

message format is incomplete, the slave does not respond.