3.2.2.1
Modbus TCP/IP diagnostic counters
Modbus TCP/IP counters can be viewed via the LHMI path
Monitoring/
Communication/Modbus/MBS0n
.
The counters show the complete Modbus protocol link frames and Modbus errors. The
Ethernet communication driver maintains its own counters for lower level
communication diagnostics.
Table 5:
TCP/IP diagnostic counters
Counter
Description
Status
Shows the value "True" if the TCP/IP or serial instance is in use. This means
that a Modbus client has connected to the TCP socket and Modbus TCP
messages are received regularly at least with a 30 second interval or faster. In
all other cases this value shows "False".
Reset counters
True = Reset all diagnostic counters
Received frames
Total amount of received Modbus frames.
Transmitted frames
Total amount of transmitted Modbus responses.
Transmitted exc A
Total amount of exception responses 1 and 2. These exception responses
usually reveal configuration errors on the Modbus client’s side.
Transmitted exc B
Total amount of exception responses 3. These exceptions reveal the IED
application level rejections.
The counters are reset when the client makes a TCP socket disconnection or if the TCP
socket connection keep alive times out.
Table 6:
Common (instance independent) Modbus TCP/IP diagnostic counters
Counter
Description
CnReject no sockets
The amount of connection requests that are rejected due to unavailable TCP
sockets.
CnReject
unregistered
The amount of connection requests that are rejected since the client is not
registered.
3.3
Supported Modbus function codes
3.3.1
Application functions
Table 7:
Supported application functions
Function
code
Name
Description
01
Read coil status
Reads the status of discrete outputs.
02
Read digital input status
Reads the status of discrete inputs.
03
Read holding registers
Reads the contents of output registers.
04
Read input registers
Reads the contents of input registers.
Table continues on next page
1MRS757645 B
Section 3
Vendor-specific implementation
620 series
19
Communication Protocol Manual
