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MVI56-MCM
♦
ControlLogix Platform
Reference
Modbus Communication Module
Page 132 of 159
ProSoft Technology, Inc.
July 24, 2008
A server device can, however, be forced into 'Listen Only Mode' in which it will
monitor the messages on the communications system but not respond to them.
This can affect the outcome of your application program if it depends upon any
further exchange of data with the remote device. Generally, the mode is forced to
remove a malfunctioning remote device from the communications system.
The following diagnostic functions are dedicated to serial line devices.
The normal response to the Return Query Data request is to loopback the same
data. The function code and sub-function codes are also echoed.
Request
Function code
1 Byte
0x08
Sub-function 2
Bytes
Data
N x 2 Bytes
Response
Function code
1 Byte
0x08
Sub-function 2
Bytes
Data
N x 2 Bytes
Error
Error code
1 Byte
0x88
Exception code
1 Byte
01 or 03 or 04
Sub-function codes supported by the serial line devices
Here the list of sub-function codes supported by the serial line devices. Each
sub-function code is then listed with an example of the data field contents that
would apply for that diagnostic.
Sub-functions supported by the MVI56-MCM module are highlighted in
BOLD
.
Sub-function code
Name
Hex Dec
00 00
Return
Query
Data
01
01
Restart Communications Option
02
02
Return Diagnostic Register
03
03
Change ASCII Input Delimiter
04
04
Force Listen Only Mode
05..09 05..09
RESERVED
0A
10
Clear Counters and Diagnostic Register
0B
11
Return Bus Message Count
0C
12
Return Bus Communication Error Count
0D
13
Return Bus Exception Error Count
0E
14
Return Slave Message Count
0F
15
Return Slave No Response Count
10
16
Return Slave NAK Count
11
17
Return Slave Busy Count