Configuration as a Modbus Master MVI56E-MCM ♦ ControlLogix Platform
User Manual Modbus Communication Module
Page 50 of 209 ProSoft Technology, Inc.
None - No Change is made in the byte ordering
(1234 = 1234)
Words - The words are swapped (1234=3412)
Words & Bytes - The words are swapped then
the bytes in each word are swapped
(1234=4321)
Bytes - The bytes in each word are swapped
(1234=2143)
Sends the command to Node #1.
Issues a Modbus Function Code 3 to "Read Holding registers."
Along with the Function Code 3, DevAddress 256 will read
Modbus address 40257 of the Slave device.
Along with the Function Code 3, DevAddress 256 will read Modbus address
40257 of the Slave device. The above command will read 40257 and 40258 of
the Modbus Slave #1 and place that data in MCM.DATA.READDATA[0] and [1].
Within the controller tags section of the ControlLogix processor, it is necessary to
configure a tag with the data type of "REAL" as shown in the following illustration.
Copy data from the MCM.DATA.READDATA[0] and [1] into the tag
ENERGY_CONSUMPTION that has a data type of REAL. Use a COP statement
within the ladder logic. Here is an example.
Because the tag MCM.DATA.READDATA[0] should only be used within the above
command, an unconditional COP statement can be used.
Notice the length of the COP statement is a value of 1. Within a Rockwell
Automation processor, a COP statement will copy the required amount of
"Source" values to fill the "Dest" tag for the Length specified.
Therefore, the above statement will copy ReadData[0] and [1] to fill the 32 bits
required for the tag "Energy_Consumption".
Note: Do not use a MOV statement. A MOV will convert the data from the Source register to the
destination register data type. This would create a data casting statement and will result in the loss
or corruption of the original data.
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