ProSoft Technology MVI69L-MBTCP - Manual (Page 139)

MVI69L-MBTCP ♦ CompactLogix Platform Reference
Communication Module User Manual
ProSoft Technology, Inc. Page 139 of 152
January 6, 2014
7.4.12 Pass-through Formatted Block for Functions 6 and 16 with
Word Data Block
Block 9956: Pass-through Formatted Block for Functions 6 and 16 with Word
Data Block
If the server port on the module is configured for formatted pass-through mode,
the module will send input image blocks with identification codes of 9956, 9957,
9958 or 9959 to the processor for each write command received. Any incoming
Modbus Function 5, 6, 15 or 16 command will be passed from the port to the
processor using a block identification number that identifies the Function Code
received in the incoming command.
The MBTCP Add-On Instruction will handle the receipt of all Modbus write
functions and to respond as expected to commands issued by the remote
Modbus Client device.
Note: Mutual exclusion on Pass-Through Block IDs 9956, 9957, 9958, and 9959 from all server
connections - When multiple server connections are active and they receive write commands with
the same Function Code, the same block identifier from the above list is needed. The module will
process the command from the server which first received a command.
The module will return an Exception Code error code 6 (Node is busy - retry command later error)
from the other server that received the command last. The Client will retry the command on the
busy port after a short delay. This prevents Pass-Through blocks on multiple servers from
overwriting each other.
Block 9956: Request from Module to Processor
Offset Description
0 Block ID 9956
1 Block ID 9956
2 Number of word registers in Modbus data set
3 Starting address for Modbus data set
4 to 53 Modbus Data
The ladder logic will be responsible for parsing and copying the received
message and performing the proper control operation as expected by the Client
device. The processor must then respond to the pass-through control block with
an output image write block with the following format.
This informs the module that the command has been processed and can be
cleared from the pass-through queue.