Modbus™ Communication DECS-200
7-6
NOTE
Variables changed by this function will not be directly saved to nonvolatile memory (EEPROM). If
specific categories (one or more) of data have to be saved to EEPROM, then Holding Register 48161
(Data Id=13001, variable “SaveCommand”) has to be preset after a category has been changed. The
exceptions to this rule are only those Holding Registers dealing with communication port RS-485.
They will be changed and immediately saved to EEPROM with the function FC16.
Loop Back Diagnostic Test (FC= 8) with Diagnostic Sub-function, Return Query Data
This query contains data to be returned (looped back) in the response. The response and query
messages should be identical. If the query is a broadcast (device address = 0), no response message is
returned.
Device
Address
Function
Code =
08 (hex)
Sub-function
High
00
Sub-function
Low
00
Data High
XX
(don’t care)
Data Low
XX
(don’t care)
CRC
Low
CRC
High
Loop Back Diagnostic Test with Diagnostic Sub-function, Restart Communications Option
This query causes the remote communications function of the DECS-200 to restart, terminating an active
listen only mode of operation. No effect is made upon primary relay operations. Only the remote
communications function is affected. If the query is a broadcast (device address of 0), no response
message is returned.
If the DECS-200 receives this query while in the listen only mode (LOM), no response message is
generated. Otherwise, a response message identical to the query message is transmitted prior to the
communications restart.
Device
Address
Function
Code =
08 (hex)
Sub-function
High
00
Sub-function
Low
01
Data High
XX
(don’t care)
Data Low
XX
(don’t care)
CRC
Low
CRC
High
Loop Back Diagnostic Test with Diagnostic Sub-function, Force Slave to Listen Only Mode
This query forces the addressed DECS-200 to the listen only mode for Modbus communications, isolating
it from other devices on the network.
While in Listen Only Mode (LOM), received data is monitored (but no responses are transmitted). The
only query that will be recognized and processed while in LOM is a maintenance restart command
(function Code 8, diagnostic code 1).
When the DECS-200 receives the restart communications query, the Listen Only mode is terminated.
Device
Address
Function
Code =
08 (hex)
Sub-function
High
00
Sub-function
Low
04
Data High
XX
(don’t care)
Data Low
XX
(don’t care)
CRC
Low
CRC
High
DATA FORMATS
DECS-200 data does not need to be converted into any special format for transmission over a Modbus
network.
Modbus Registers hold original DECS-200 data of the generic (built-in) data types listed in Table 7-4.
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