5.6.3 Diagnostics (loopback test) [08H]. RKC INSTRUMENT SA200

5. MODBUS COMMUNICATION PROTOCOL

5.6.3 Diagnostics (loopback test) [08H]

The master’s query message will be returned as the response message from the slave. This function checks the communication system between the master and slave.

Example: Loopback test for slave address 1

Query message

Slave address

Function code

Test code

Data

CRC-16

High

Low

High

Low

High

Low

01H

08H

00H

00H

1FH

34H

E9H

ECH

Test code must be set to 00

Any pertinent data

Normal response message

Slave address

Function code

Test code

Data

CRC-16

High

Low

High

Low

High

Low

Error response message

Slave address

80H + Function code

Error code

CRC-16 High

Low

01H

88H

03H

06H

01H

01H

08H

00H

00H

1FH

34H

E9H

ECH

Contents will be the same as query message data.

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