ProSoft Technology MVI56E-MNETC - Manual (Page 129)

MVI56E-MNETC ♦ ControlLogix Platform Reference
Modbus TCP/IP Client Enhanced Communication Module User Manual
ProSoft Technology, Inc. Page 129 of 183
February 3, 2013
Command Control Blocks (5001-5016)
Note: Command Control is not needed for normal Modbus command list polling
operations and is needed only occasionally for special circumstances.
During routine operation, the module continuously cycles through the user-
defined MNET Client x Command List (page 51) for each Client, examining
commands in the order they are listed, and sending enabled commands on the
network. However, the module also has a special command priority queue, which
is an internal buffer that holds commands from special function blocks until they
can be sent on the network.
When one or more commands appear in the command priority queue:
1 The routine polling process is temporarily interrupted.
2 The commands in the command priority queue are executed until the queue
is empty.
3 Then the module goes back to where it left off on the MNET Client x
Command List and continues routine polling.
Like Event Command blocks, Command Control blocks place commands into the
module’s command priority queue. Unlike Event Command blocks, which contain
all the values needed for one command, Command Control is used with
commands already defined in the MNET Client x Command List.
Commands in the MNET Client x Command List may be either enabled for
routine polling or disabled and excluded from routine polling. A disabled
command has its bit in the MNETC.CONTROL.CmdControl.WriteCmdBits
controller tag set to zero (0) and is skipped during routine polling. An enabled
command has its bit in the WriteCmdBits controller tag set to one (1) and is sent
during routine polling. However, Command Control allows any command in the
predefined MNET Client x Command List to be added to the command priority
queue, whether it is enabled for routine polling or not.
Command Control also gives you the option to use ladder logic to have
commands from the MNET Client x Command List executed at a higher priority
and out of routine order, if such an option might be required in special
circumstances.
A single Command Control block request can place up to 16 commands from the
MNET Client x Command List into the command priority queue.
Block Request from Processor to Module
Word Offset Description Length
0 Command Control block identification code of 5001 to 5016. The
rightmost digit indicates the number of commands (1 to 16) to
add to the command priority queue. 1
1 Client index 1
2 This word contains the Command Index for the first command to
be entered into the queue. 1
3 Command Index 2 1