MVI56-MCM ♦ ControlLogix Platform Reference
Modbus Communication Module
Page 96 of 159 ProSoft Technology, Inc.
July 24, 2008
remote slave device to be associated with the command. When the command
receives the block, it will process it and place it in the command queue. The
module will respond to each event command block with a read block with the
following format:
Offset Description Length
0 Reserved 1
1 Write Block ID 1
2 0 = Fail, 1 = Success 1
3 to 248 Spare 246
249 1000 to 1255 or 2000 to 2255 1
Word two of the block can be used by the ladder logic to determine if the
command was added to the command queue of the module. The command will
only fail if the command queue for the port is full (100 commands for each
queue).
Command Control
Command control blocks place commands in the command list into the command
queue. Each port has a command queue of up to 100 commands. 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.
Offset Description Length
0 5001 to 5006 or 5101 to 5106 1
1 Command index (MCM.CONFIG.PortXMasterCmd [command index value]) 1
2 Command index (MCM.CONFIG.PortXMasterCmd [command index value]) 1
3 Command index (MCM.CONFIG.PortXMasterCmd [command index value]) 1
4 Command index (MCM.CONFIG.PortXMasterCmd [command index value]) 1
5 Command index (MCM.CONFIG.PortXMasterCmd [command index value]) 1
6 Command index (MCM.CONFIG.PortXMasterCmd [command index value]) 1
7 to 247 Spare 241
Blocks in the range of 5001 to 5006 are used for Modbus Port 1, and blocks in
the range of 5101 to 5106 are used for Modbus Port 2. The last digit in the block
code defines the number of commands to process in the block. For example, a
block code of 5003 contains 3 command indexes that are to be used with
Modbus Port 1. The Command index parameters in the block have a range of 0
to 99 and correspond to the master command list entries.
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