MVI56E-MCM ♦ ControlLogix Platform Reference
Modbus Communication Module User Manual
ProSoft Technology, Inc. Page 129 of 209
When the command receives the block, it will process it and place it in the
command queue. The module will respond to each command block with a read
block. The following table describes the format of this block.
Block Response from Module to Processor
1000 to 1255 or 2000 to 2255
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 (325 commands for each queue
for modules with firmware version 3.01 or higher and Add-on-Instruction version
2.8 or higher).
Slave Status Blocks (3000 to 3003 or 3100 to 3103)
Slave status blocks send status information of each Slave device on a Master
Port. Slaves attached to the Master Port can have one of the following states:
The Slave is inactive and not defined in the command list for the Master Port.
The Slave is actively being polled or controlled by the Master Port. This does not
indicate that the Slave has responded to this message.
The Master Port has failed to communicate with the Slave device. Communications
with the Slave is suspended for a user defined period based on the scanning of the
command list.
Communications with the Slave has been disabled by the ladder logic. No
communication will occur with the Slave until this state is cleared by the ladder
logic.
Slaves are defined to the system when the module initializes the Master
command list. Each Slave defined will be set to a state of one in this initial step. If
the Master Port fails to communicate with a Slave device (retry count expired on
a command), the Master will set the state of the Slave to a value of 2 in the
status table. This suspends communication with the Slave device for a user
specified scan count (ERRORDELAYCNTR value in the MCMPORT object for each
port). Each time a command in the list is scanned that has the address of a
suspended Slave, the delay counter value will be decremented. When the value
reaches zero, the Slave state will be set to one. This will enable polling of the
Slave.
Request for first 128 Slave status values for Modbus Port 1
Request for last 128 Slave status values for Modbus Port 1
Request for first 128 Slave status values for Modbus Port 2
Request for last 128 Slave status values for Modbus Port 2
The following table describes the format of these blocks.
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