Interface and Menus
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Publication S177E V2.0 Issue 12/04
8.7.2
Modbus Port Diagnostic Displays
Port number
1 msg err xcpt crc
Message counts
123 0 0 0
Mod func addr data
Last message details
1 2 1920 48
The illustration shows the diagnostic display for Port 1, the display for Port 2 is similar.
These screens give detailed diagnostic information for the serial links; the Port number is shown on
the top line. The top half displays numerical count for various message types since the last time the
display was reset (cleared to 0):
msg
- number of valid messages received
err
- number of errors, e.g. overrun errors, parity errors, Baud rate errors
xcpt
- number of Modbus exception responses generated
crc
- number of messages received with incorrect CRC's
The bottom half shows details of the last message received, (the address and data in decimal format):
Mod
- the Modbus address of the last request
func
- the Modbus function code of the last request
addr
- the discrete bit or register number in the last request
data
- the data field of the last request, typically the number of points or registers
Some familiarity with the protocol is needed to make use of this display. Its purpose is help in
commissioning a serial communications link to a Host computer by making the master station show
the received data as it interpreted it. By referring to the protocol specification the validity of the
messages can be checked. The display is normally 'frozen' and is only updated when a key is pressed
(any key except the Menu key). This gives time to take note of the numbers. Most Host systems are
set up to send out a short sequence of requests for data, and by pressing a key a few times it is
possible to capture all the messages. The "Clear" key resets the counters on the top half of the
screen.
Commands available:
-
Zeros the message and error counts
-
Or any other key except Clear or Menu updates display with the last
message
-
Return to previous menu
MENU
LOAD
CLEAR
