Read Holding Register - Function Code 03 - ABB C250 User Manual

...5 MODBUS Functions
5.2 Read Holding Register – Function Code 03
5.2.1 Read Holding Register Query
The Read Holding Register Query obtains the contents of up to eight holding registers
in the addressed slave.
Note. The data start register must contain the offset address of the first
register to be accessed, e.g. to start at register 1 the data start register
must contain 00 (00H).
Broadcast mode is not supported by Function Code 03.
Example. Read three holding registers from slave (01) starting at holding address 01
(process variable input).
Address Function
01 03
5.2.2 Read Holding Register Response
The addressed slave responds with its address and function code, followed by the
information field. The information field contains one byte describing the quantity of
data bytes to be returned. Two bytes are used to return each register requested, the
first byte containing the high order bits and the second the low order bits.
Example
PV input (two registers)
PV decimal places
Address Function Count Register 01
01 03
10
Register Register Data No. of
Start Start
Offset High Offset Low
00 00
– 270
–
Byte Holding
High Low
00 00 00
Registers
High
00
1
Holding
Register 02 Register 03
High Low High Low
01 09
Data No. of Error
Registers Check ( C R C - 1 6 )
Low Field
03 05
Holding Error
Check ( C R C - 1 6 )
Field
00 01 49
CB
75