Technical data

Fieldbus Communication • 215
MODBUS Functions
WAGO-I/O-SYSTEM 750
BACnet/IP Controller
Therefore the MODBUS protocol based essentially on the following basic
data types:
Data type Length Description
Discrete Inputs 1 Bit Digital Inputs
Coils 1 Bit Digital Outputs
Input Register 16 Bit Analog-Input data
Holding Register 16 Bit Analog-Output data
For each basic data type one or more „Function codes“ are defined.
These functions allow digital or analog input and output data, and internal
variables to be set or directly read out of the fieldbus node.
Function code
hexadec.
Function
Access method and
description
Access to resources
FC1:
0x01 Read Coils Reading of several
single input bits
R: Process image, PFC variables
FC2:
0x02 Read Input
Discretes
Reading of several
input bits
R: Process image, PFC variables
FC3:
0x03 Read Multiple
Registers
Reading of several
input registers
R: Process image, PFC variables, in-
ternal variables, NOVRAM
FC4:
0x04 Read Input
Registers
Reading of several
input registers
R: Process image, PFC variables, in-
ternal variables, NOVRAM
FC5:
0x05 Write Coil Writing of an indi-
vidual output bit
W: Process image, PFC variables
FC6:
0x06 Write Single
Register
Writing of an indivi
d
ual output register
W: Process image, PFC variables, in-
ternal variables, NOVRAM
FC 11:
0x0B Get Comm
Event Count-
ers
Communication
event counter
R: None
FC 15:
0x0F Force Multiple
Coils
Writing of several
output bits
W: Process image, PFC variables
FC 16:
0x0010 Write Multi
p
le
Registers
Writing of several
output registers
W: Process image, PFC variables, inter-
nal variables, NOVRAM
FC 22:
0x0016 Mask Write
Register
W: Process image, PFC variables,
N
OVRAM
FC 23:
0x0017 Read/Write
Registers
Reading and writ-
ing of several out-
put registers
R/W: Process image, PFC variables,
N
OVRAM
Tab. 4-3: List of the MODBUS Functions in the Fieldbus Controller
To execute a desired function, specify the respective function code and the
address of the selected input or output data.
Attention
The examples listed use the hexadecimal system (i.e.: 0x000) as their numerical
format. Addressing begins with 0.
The format and beginning of the addressing may vary according to the software
and the control system. All addresses then need to be converted accordingly.