WAGO I/O-SYSTEM 750, Manual, Page: 225 / 450

WAGO-I/O-SYSTEM 750 Fieldbus Communication 225
750-882 Media Redundancy ETHERNET Controller
Manual
1.5.0
More information
More information on the “Open MODBUS/TCP specification” you can find in the
Internet: www.modbus.org .
Therefore the MODBUS protocol based essentially on the following basic data
types:
Table 86: Basic Data Types of MODBUS Protocol
Data type Length Description
Discrete inputs 1 bit Digital inputs
Coils 1 bit Digital outputs
Input register 16 bits Analog input data
Holding register 16 bits 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.
Table 87: List of the MODBUS Functions in the Fieldbus Coupler
Function code
Function Access method and description
Access to resources
(R=read/W=write)
Desig-
nation
Value
(hex)
FC1 0x01 Read Coils Reading of several output bits R: Process image,
PFC variables
FC2 0x02 Read Discrete
Inputs
Reading of several input bits R: Process image,
PFC variables
FC3 0x03 Read Holding
Registers
Reading of several input registers R: Process image,
PFC variables,
internal variables,
NOVRAM
FC4 0x04 Read Input
Registers
Reading of several input registers R: Process image,
PFC variables,
internal variables,
NOVRAM
FC5 0x05 Write Single
Coil
Writing of an individual output bit W: Process image,
PFC variables
FC6 0x06 Write Single
Register
Writing of an individual output
register
W: Process image,
PFC variables,
internal variables,
NOVRAM
FC11 0x0B Get Comm
Event Counters
Communication event counter R: None
FC15 0x0F Write Multiple
Coils
Writing of several output bits W: Process image,
PFC variables
FC16 0x10 Write Multiple
Registers
Writing of several output registers W: Process image,
PFC variables,
internal variables,
NOVRAM
FC22 0x16 Mask Write
Register
Writing of several bits of an
individual output register by mask
W: Process image,
PFC variables,
NOVRAM