Preset Single Register - Function Code 06; Preset Single Register Query; Preset Single Register Response; Loopback Test - Function Code 08 - ABB C1900 Installation Manual

Circular chart recorder and recorder/controller, modbus (rtu) communications option

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5.4

Preset Single Register – Function Code 06

5.4.1

Preset Single Register Query

The preset single register allows the user to modify the contents of a holding register.

Note. Function codes 5, 6 and 16 are the only messages that are recognized as valid for broadcast.

Example – a preset single register request to write the value 500 to holding register address 121 (alarm trip A1) in slave 01 is

shown below.

Note. To write to a register, the register's offset address must be used, e.g. to write to register 121, the offset address

120(78H) is transmitted.

Address

Function

5.4.2 Preset Single Register Response

The normal response to a preset single register request is to retransmit the query message after the register has been altered.

Example

Address

Function

5.5

Loopback Test – Function Code 08

5.5.1

Loopback Test Query

The purpose of the loopback test is to test the Modbus system, it does not affect the content of the controller. Variations in the

response may indicate faults in the Modbus system. The information field contains 2 bytes for the designation of the diagnostic

code followed by 2 bytes to designate the action to be taken.

Example

Data Diagnostic

Address

Function

*These are considered to be the information fields for diagnostic mode.

5.5.2

Loopback Test Response

The response always echoes the query, only diagnostic code 0 (bytes 3 and 4) can be used.

Example

Data Diagnostic

Address

Function

Offset High

Offset Low

Offset High

Offset Low

Data Diagnostic

Code High

Code Low

Data Diagnostic

Code High

Code Low

Data Value High

Data Value Low

Data Value High

Data Value Low

Data*

Data *

Data

5 MODBUS FUNCTIONS...

Error Check Field (CRC-16)

Data

Error Check Field (CRC-16)

Table of Contents

Preset Single Register - Function Code 06; Preset Single Register Query; Preset Single Register Response; Loopback Test - Function Code 08 - ABB C1900 Installation Manual

Preset Single Register Query

5.4.2 Preset Single Register Response

Loopback Test Query

Loopback Test Response

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