Loopback Test; Loopback Test Query; Loopback Test Response; Preset Multiple Registers - ABB 8241 Operating Instructions Manual

...8 MODBUS FUNCTIONS
8.5 Loopback Test – Function Code 08

8.5.1 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:
Address
Function
01 08

8.5.2 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
01 08
*These are considered to be the information fields for diagnostic mode.
8.6 Preset Multiple Registers – Function Code 16

8.6.1 Preset Multiple Registers Query

Holding registers existing within the controller can have their contents changed by this message. When used with slave address
zero (Broadcast mode) all slave controllers load the selected registers with the contents specified.
Note. To write to multiple registers, the initial register offset address must be used, e.g. to write to register 02 onwards,
the offset address 01 is transmitted.
Example – a preset multiple registers request to write the value 1000 to the register address (Output Range 1) and the value 2000
to the register address (Output Range 2) in slave 01 is shown below.
Register
Start
Address Function
Offset
High
01 10 00

8.6.2 Preset Multiple Registers Response

The response confirms slave identification, function code, starting register address and quantity only.
Example:
Address
Function
01 10
Register Register
Offset High Offset Low
00 31
Data Diagnostic
Code Low
Code High
00 31
Register
Number
Start
Byte
of
Offset
Count
Registers
Low
31 00 02 04
Register Start Register Start
Offset High Offset Low
00 31
Data Value High Data Value Low
04 02
Data * Data *
04
Holding Holding Holding
Register Register Register
02 High 02 Low 03 High
08 00
Number of Registers
00
Error Check Field (CRC-16)
32
Error Check Field (CRC-16)
02 32
Holding
Error Check Field
Register
(CRC-16)
03 Low
0F FF 76
Error Check Field (CRC-16)
02 10
C5
C5
A7
07
11