MVI56-MCM ♦ ControlLogix Platform Reference
Modbus Communication Module
Page 104 of 159 ProSoft Technology, Inc.
July 24, 2008
Master Command List
In order to function in the Master Mode, the module's Master Command List must
be defined. This list contains up to 100 individual entries, with each entry
containing the information required to construct a valid command. This includes
the following:
Command enable mode ((0) disabled, (1) continuous or (2) conditional)
Slave Node Address
Command Type - Read or Write up to 125 words (2000 bits) per command
Database Source and Destination Register Address - Determines where data
will be placed and/or obtained
Count - Select the number of words to be transferred - 1 to 125 on FC 3, 4, or
16. Select the number of bits on FC 1, 2, 15.
As the list is read in from the processor and as the commands are processed, an
error value is maintained in the module for each command. You can view the
current command error list (page 79) from the module's Config/Debug menu.
The errors generated by the module are displayed in the following tables.
Standard Modbus Protocol Errors
Code Description
1 Illegal Function
2 Illegal Data Address
3 Illegal Data Value
4 Failure in Associated Device
5 Acknowledge
6 Busy, Rejected Message
Module Communication Error Codes
Code Description
-1 CTS modem control line not set before transmit
-2 Timeout while transmitting message
-11 Timeout waiting for response after request
253 Incorrect slave address in response
254 Incorrect function code in response
255 Invalid CRC/LRC value in response
Command List Entry Errors
Code Description
-41 Invalid enable code
-42 Internal address > maximum address
-43 Invalid node address (< 0 or > 255)
-44 Count parameter set to 0
-45 Invalid function code
-46 Invalid swap code
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