ProSoft Technology MVI56E-MCMR - Manual (Page 159)

MVI56E-MCMR ♦ ControlLogix Platform Reference
Modbus Communication Module with Reduced Data Block User Manual
ProSoft Technology, Inc. Page 159 of 225
May 13, 2014
Block Response from Module to Processor
Word Offset Definitions
0 9901 or 9911 Event Command ID number
1 0 = Fail-command not added to the command queue,
1 = Success-command added to the command queue.
2 Reserved for future use (will always be zero)
3 Reserved for future use (will always be zero)
4 Reserved for future use (will always be zero)
Please note that the status returned in Word 1 indicates only that the command
received from the Send Event Command MSG was considered a valid command
and was successfully added to the top of the Command Queue as the next
command to be sent. A "Success" result in this data block does not indicate:
 Whether the command was successfully sent on the Modbus Network
 Whether the Slave received or responded to the command
 Whether the Slave's response (in any) was valid
There are many potential reasons why a command might fail after having been
successfully added to the Command Queue. For more details, see Standard
Modbus Protocol Errors or Module Communication Error Codes.
Command Control Blocks (9902 or 9912)
The Command Control special function is applicable only when the module's port
is configured as a Modbus Master. Command Control is best used to send
commands based on special process conditions, such as emergency shutdowns,
device-specific resets or any conditions which might require priority polling of a
specific Slave Device. Whenever a Command Control data block is received by
the module, it will insert the requested command or commands into the beginning
of the Command Queue, so that the special command or commands will be sent
before the next regular polling command.
Sending a message (MSG instruction) containing Command Control Block
Identification Code 9902 for Port 1 or 9912 for Port 2 will cause a list of from one
(1) to twenty (20) commands to be placed in the Command Queue using
commands from the user-created PCB Command Lists. These lists are the ones
created in the M
ODBUS P ORT 1 C OMMANDS or M ODBUS P ORT 2 C OMMANDS
sections of the PCB configuration file that was downloaded to the module and
that are used by the module for normal, automatic, repetitive polling.
Any command in the Command List may be given execution priority using a
Command Control special function block MSG, regardless of the value set in the
E
NABLE parameter for that command. However, commands placed in the
Command List intended for exclusive use with Command Control will most often
have their E
NABLE parameter set to zero(0) and will not be executed as part of a
regular polling routine. Commands enabled using Command Control will be
added to the Command Queue for a one-time execution each time the MSG
instruction is activated.