ProSoft Technology MVI69-MCM - Manual (Page 59)

MVI69-MCM ♦ CompactLogix or MicroLogix Platform Configuring the MVI69-MCM Module
Modbus Communication Module User Manual
ProSoft Technology, Inc. Page 59 of 167
March 22, 2011
2.4.4 [Modbus Port x Commands]
The [Modbus Port x Commands] section of the configuration file defines the
command list specifications for the Master port. The information in this section
applies to both Port 1 and Port 2.
Command List Overview
In order to interface the MVI69-MCM module with MODBUS slave devices, you
must construct a command list. The commands in the list specify the slave
device to be addressed, the function to be performed (read or write), the data
area in the device to interface with and the registers in the internal database to
be associated with the device data. The Master command list supports up to 100
commands.
The command list is processed from top (command #0) to bottom. A poll interval
parameter is associated with each command to specify a minimum delay time in
number of seconds between the issuance of a command. If the user specifies a
value of 10 for the parameter, the command will be executed no more frequently
than every 10 seconds.
Write commands have a special feature, as they can be set to execute only if the
data in the write command changes, which can improve network performance. If
the register data values in the command have not changed since the command
was last issued, the command will not be executed. To enable this feature, set
the enable code for the command to a value of 2.
Modbus Command Configuration
The ProSoft Technology MCM Modbus Master and Slave communication drivers
support several data read and write commands. When configuring a Master port,
the decision on which command to use is made depending on the type of data
being addressed, and the level of Modbus support in the slave equipment. When
configuring as a slave, it may be important to understand how the Modbus
commands function in order to determine how to structure the application data.