Owner's manual

Appendix C _________________________________________________________ Modbus Reference
VAISALA _______________________________________________________________________ 183
Diagnostic Sub-Functions
DMT345/346 support some of the Modbus diagnostic functions
described in the Modbus Application Protocol Specification V1.1b.
These diagnostic functions are accessed with function code 08. See Table
53 below for details.
Table 53 Modbus Diagnostics
Code
Sub-Function Name
Notes
00 (0x00)
Return Query Data
01 (0x01)
Restart Communications
Option
Cancels the “Listen Only” mode.
Data field must be set to “00 00”
for Restart Communications
Option. Sub-Function 01 with
data field “FF 00” is rejected.
02 (0x02)
Return Diagnostic Register
Non-zero if there are active
transmitter errors.
For same error information, see
status registers 0516 and 0517.
The value of the Diagnostic
Register is a logical OR of these
two status registers.
04 (0x04)
Force Listen Only Mode
Puts device “off-line”
10 (0x0A)
Clear Counters and
Diagnostic Register
Diagnostic Register cannot be
cleared
11 (0x0B)
Return Bus Message Count
Total number of messages seen
on the bus/interface
12 (0x0C)
Return Bus Communication
Error Count
Number of messages with bad
Modbus RTU CRC or Modbus
TCP frame
13 (0x0D)
Return Bus Exception Error
Count
Number of Modbus exception
responses sent
14 (0x0E)
Return Slave Message Count
Number of Modbus messages
processed
15 (0x0F)
Return Slave No Response
Count
Number of Modbus messages
received without sending a
response. This happens for
received broadcast messages
(Modbus RTU only) or when
DMT345/346 is in the “Listen
Only” mode.
Although Modbus Diagnostics are standardized only for serial line
devices, DMT345/346 supports the same diagnostic functions also on
Modbus TCP.
NOTE
Resetting, powering up the transmitter, or reselecting the
Modbus mode
(by serial command or with the user interface) resets all
Modbus
diagnostic counters and cancels any “Listen Only” mode.