ProSoft Technology MVI56E-MCM/MCMXT - Manual (Page 125)

MVI56E-MCM ♦ ControlLogix Platform Reference
Modbus Communication Module User Manual
ProSoft Technology, Inc. Page 125 of 199
June 18, 2014
Ladder logic can be written to override the value in the Slave status table to
enable the Slave (state value of 1) by sending a special block. Port 1 Slaves are
enabled using block 3001, and Port 2 Slaves are enabled using block 3101. Each
block contains the Slave node addresses to enable. The following table
describes the format for this block.
Block Request from Processor to Module
Word Offset Description Length
0 3001 or 3101 1
1 Number of Slaves in Block 1
2 to 201 Slave indexes 200
202 to 247 Spare 46
The module will respond with a block with the same identification code received
and indicate the number of Slaves acted on with the block. The following table
describes the format of this response block.
Block Response from Module to Processor
Word Offset Description Length
0 Reserved 1
1 Write Block ID 1
2 Number of Slaves processed 1
3 to 248 Spare 246
249 3001 or 3101 1
Command Control Blocks (5001 to 5006 or 5101 to 5106)
Command Control blocks place commands in the command list into the
command queue. Each port has a command queue of up to 325 commands (for
modules with firmware version 3.01 or higher and Add-on-Instruction version 2.8
or higher). The module services commands in the queue before the Master
command list. This gives high priority to commands in the queue. Commands
placed in the queue through this mechanism must be defined in the Master
command list. Under normal command list execution, the module will only
execute commands with the Enable parameter set to one or two. If the value is
set to zero, the command is skipped. Commands may be placed in the command
list with an Enable parameter set to zero. These commands can then be
executed using the Command Control blocks.
One to six commands can be placed in the command queue with a single
request. The following table describes the format for this block.