Modbus Function Codes - ABB COMMANDER 100 Operating Manual

...4 MODBUS PROTOCOL

4.2 MODBUS Function Codes

The function code instructs the addressed slave which function to perform.
Table 4.1 shows the function codes, and describes the action they initiate.
Function
Code
01
Coil Status
03
Holding Register
05
Single Coil
06
Single Register
Loop Back
08
16
Registers
*NAK = Negative Acknowledgment
8
Function
Title
Read Read up to 16 consecutive discrete (Boolean) points
from a specific starting point. The slave instrument
returns zeros for points which do not contain defined
data and NAKs* any request for point numbers
greater than 60.
Read
Read up to 8 consecutive registers from a specific
starting register. The slave instrument returns zeros
for points which do not contain defined data and
NAKs* any request for point numbers greater than
90.
Force
Write one discrete (Boolean) point. The slave
instrument NAKs* this if the point is not currently
writeable.
Preset
Write one register. This code also applies any
existing limits to the register before storage in the
instrument. The slave instrument NAKs* if the
register is not currently writeable.
Echo the message. Only 'Return of Query' is
supported.
Write up to eight consecutive registers from a
Preset
specified starting register. The slave instrument
Multiple
NAKs* if any of the registers are not currently
writeable, but carries out all the writes which are
valid, applying any existing limits to the value before
storage in the instrument.
Table 4.1 MODBUS Function Codes
Description