Function Code Fc3 (Read Multiple Registers); Table 97: Request Of Function Code Fc3; Table 98: Response Of Function Code Fc3; Table 99: Exception Of Function Code Fc3 - WAGO -I/O-SYSTEM 750 Manual

WAGO-I/O-SYSTEM 750
750-882 Media Redundancy ETHERNET Controller
12.2.3.3

Function Code FC3 (Read Multiple Registers)

This function reads the contents of holding registers from a slave device in word
format.
Request
The request specifies the reference number (start register) and the word count
(register quantity) of the registers to be read. The reference number of the
request is zero based, therefore, the first register starts at address 0.
Example: Read registers 0 and 1.

Table 97: Request of Function Code FC3

Byte
Byte 0, 1
Byte 2, 3
Byte 4, 5
Byte 6
Byte 7
Byte 8, 9
Byte 10, 11
Response
The reply register data is packed as 2 bytes per register. The first byte contains
the higher value bits, the second the lower values.

Table 98: Response of Function Code FC3

Byte
...
Byte 7
Byte 8
Byte 9, 10
Byte 11, 12
The contents of register 0 are displayed by the value 0x1234 and the
contents of register 1 is 0x2345.
Exception

Table 99: Exception of Function Code FC3

Byte
...
Byte 7
Byte 8
Field name
Transaction identifier
Protocol identifier
Length field
Unit identifier
MODBUS function code
Reference number
Word count
Field name
MODBUS function code
Byte count
Value register 0
Value register 1
Field name
MODBUS function code
Exception code
Fieldbus Communication 233
Example
0x0000
0x0000
0x0006
0x01 not used
0x03
0x0000
0x0002
Example
0x03
0x04
0x1234
0x2345
Example
0x83
0x01 or 0x02
Manual
1.5.0