Technical data

154 • MODBUS Functions
Description of the MODBUS Functions
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP
6.3.7 Function Code FC11 (Get comm event counter)
This function returns a status word and an event counter from the slave
device’s communication event counter. By reading the current count before
and after a series of messages, a master can determine whether the messages
were handled normally by the slave.
Following each successful new processing, the counter counts up. This
counting process is not performed in the case of exception replies, poll
commands or counter inquiries.
Request
Byte Field name Example
Byte 0, 1 Transaction identifier 0x0000
Byte 2, 3 protocol identifier 0x0000
Byte 4, 5 length field 0x0002
Byte 6 unit identifier 0x01 not used
Byte 7 MODBUS function code 0x0B
Response
The reply contains a 2-byte status word and a 2-byte event counter. The status
word only contains zeroes.
Byte Field name Example
.....
Byte 7 MODBUS function code 0x0B
Byte 8, 9 Status 0x0000
Byte 10, 11 Event Count 0x0003
The event counter shows that 3 (0x0003) events were counted.
Exception
Byte Field name Example
.....
Byte 7 MODBUS function code 0x85
Byte 8 Exception code 0x01 or 0x02