MVI56-MCM ♦ ControlLogix Platform Configuration as a Modbus Master
Modbus Communication Module
Page 26 of 159 ProSoft Technology, Inc.
July 24, 2008
4.2 ModDef Settings
The first step in the configuration of the module is in the tag labeled
MCM.CONFIG.ModDef. This will setup which of the 5000 data registers will be
written to the MVI module, and which of the 5000 data registers will be read from
the MVI module. The read and write data locations will be used later in the
Master Command section when we configure the IntAddress within each
MasterCommand. Below are the values from our sample ladder program.
The WriteStartReg will be used to determine the starting register location for
WriteData [0 to 599] and the WriteRegCnt will be used to determine how many
of the 5000 registers will be used for information to be written out to the module.
The sample ladder file will setup 600 registers for write data, labeled
MCM.WriteData[0 to 599].
Label Description
WriteStartReg
Determines where in the 5000 register module memory to place the
data obtained from the ControlLogix processor from the WriteData tags.
WriteRegCnt
Sets how many registers of data the MVI module will request from the
CLX processor. Because the module pages data in blocks of 200
words, this number should be evenly divisible by 200.
ReadStartReg
Determines where in the 5000 register module memory to begin
obtaining data to present to the CLX processor in the ReadData tags.
ReadRegCnt
Sets how many registers of data the MVI module will send to the CLX
processor. This value should also be a multiple of 200.
BPFail
Sets the consecutive number of backplane failures that will cause the
module to stop communications on the Modbus network. Typically used
when the module is configured as a slave.
ErrStatPtr
Also used mainly when the module is setup as a slave. This parameter
places the STATUS data into the database of the module.
The sample configuration values set up the module database for WriteData[0 to
599] to be stored in the module memory at register 0 to 599, and ReadData[0 to
599] to be stored in the module memory at registers 1000 to 1599 like shown
below.
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