Specifications

68
Schneider Electric
The Modbus Protocol (continued)
Read event counters: function 11
Each slave has an event counter. The master also has an event counter. This
counter is incremented by one for each frame correctly received and interpreted by
the slave (except for the specific command for reading this counter, i.e., function 11).
The counter is also incremented for a correct broadcast command. If the slave
transmits an exception response, however, the counter is not incremented.
A diagnostic of exchanges between the master and the slave can be obtained by
reading the various counters.
If the master’s counter is equal to the slave’s counter, the command sent by the
master has indeed been executed. If the master’s counter is equal to the slave’s
counter + 1, the command sent by the master has not been executed.
b Query.
b Response.
This counter tells the master:
b If the slave has correctly interpreted the
command (event counter incremented).
b If the slave has not interpreted the
command (counter not incremented).
E52374E52375
Slave No. OB CRC 16
1
b
y
te 2 b
y
tes
LSB* MSB*
1 byte 1 byte 2 bytes 2 bytes
Slave No.
OB
CRC 1600 00
Contents of
slave’s
counter
2 bytes
LSB* MSB*
Guide to Integration
Modbus / Jbus