Reference MVI56E-MCM ♦ ControlLogix Platform
User Manual Modbus Communication Module
Page 136 of 209 ProSoft Technology, Inc.
Formatted Pass-Through Blocks (9956 to 9959)
If one or more of the Slave Ports on the module are configured for the Formatted
Pass-through mode, the module will pass blocks with identification codes of 9956
to 9959 to the processor for each received write command. Any Modbus function
5, 6, 15 or 16 commands will be passed from the port to the processor using
these block identification numbers. Ladder logic must handle the receipt of all
Modbus write functions to the processor and must respond as expected to
commands issued by the remote Modbus Master device. The structure of these
formatted Pass-through blocks is shown in the following tables:
Function 5
Pass-Through Block 9958 from Module to Processor
The ladder logic will be responsible for parsing and copying the received
message and performing the proper control operation as expected by the Master
device. The processor must then respond to the Pass-through block with a write
block with the following format.
Response Block 9958 from Processor to Module
This will inform the module that the command has been processed and can be
cleared from the pass-through queue.
Function 6 and 16
Pass-Through Blocks 9956 or 9957 from Module to Processor
9956/9957 (Floating-point)
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