ProSoft Technology MVI69E-MBS - Manual (Page 142)

Reference MVI69E-MBS ♦ CompactLogix Platform
User Manual Communication Module
Page 142 of 162 ProSoft Technology, Inc.
January 6, 2014
The MBS Add-On Instruction handles the receipt of all Modbus write functions
and to respond as expected to commands issued by the remote Modbus Master
device.
Note: Mutual exclusion on Pass-Through Block IDs 9956, 9957, 9958, and 9959 from both ports -
If both ports are configured as slave ports, when both of the slave ports receive write commands
with the same Function Code, which would need to use the same block identifier from the above
list, the module processes the command from the port which first received the command.
The module returns an Exception Code error code 6 (Node is busy - retry command later error)
from the other port that received the command last. The Master retries the command on the busy
port after a short delay. This prevents Pass-Through blocks on both ports from overwriting each
other.
Block 9956: Request from Module to Processor
Offset Description
0 Read Block ID: 9956
1 Write Block ID: 9956
2 Number of word registers in Modbus data set
3 Starting address for Modbus data set
4 to (n+1) Data (Length in words = n - 2)
Where n = 60, 120, or 240 depending on the Block Transfer Size parameter.
The ladder logic is 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 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.
Block 9956: Response from Processor to Module
Offset Description
0 Write Block ID: 9956
1 to n Spare (Length in words = n - 2)