Instruction manual

5. MODBUS PROTOCOL

IMCB14-E1

5.2 Function Code

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Function code contents

Function code

(Hexadecimal)

Function Contents

03H

Read holding registers

Measured value (PV), alarm status, current

transformer input, etc.

06H

Preset single register

Set value (SV), alarm set value, PID constants,

PV bias, etc. (For each word)

08H

Diagnostics (loopback test)

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Message length of each function (Unit: byte)

Function code Function

Query message Response message

(Hexadecimal)

MinMaxMinMax

03H

Read holding registers 8 8 7 255

06H

Preset single register

8888

08H

Diagnostics (loopback test)

8888

5.3 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 5.2 Function Code

Data time interval 24 bit's time or less*

Error check CRC-16

* 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.