ProSoft Technology MVI56E-MCM/MCMXT - Manual (Page 47)

MVI56E-MCM ♦ ControlLogix Platform Configuration as a Modbus Master
Modbus Communication Module User Manual
ProSoft Technology, Inc. Page 47 of 199
June 18, 2014
The following topics show how to read or write data to a Slave device. These
topics also show when to use the Float Flag and Float Start parameters within
the module configuration. For all applications, floating-point data can be read
from a device without any changes to the Float Flag and Float Start parameters.
You only need to configure these parameters to issue a Write command to a
device that uses a single Modbus address, such as 47001, to represent a single
floating-point value.
2.4.1 Read Floating-Point Data
Here is the addressing of a Slave device, with a parameter "Energy
Consumption" that is shown as two registers 40257 and 40258.
Value Description Type
40257 -------- KWH Energy Consumption Float, lower 16 bits
40258 KWH Energy Consumption Float, upper 16 bits
To issue a Read command to this parameter, use the following configuration.
Parameter Value Description
Enable 1 Sends the command every time through the command list.
IntAddress 1000 Places data at address 1000 of the module memory. Based on the
configuration in ModDef this will put the data at the tag
MCM.DATA.R
EAD D ATA [0].
PollInt 0 No delay for this command.
Count 2 Reads 2 consecutive registers from the Slave device. These 2
Modbus registers will make up the "Energy Consumption" floating-
point value.
Swap 0 Swap Code Description
0 None - No Change is made in the byte ordering
(1234 = 1234)
1 Words - The words are swapped (1234=3412)
2 Words & Bytes - The words are swapped then
the bytes in each word are swapped
(1234=4321)
3 Bytes - The bytes in each word are swapped
(1234=2143)
Node 1 Sends the command to Node #1.
Func 3 Issues a Modbus Function Code 3 to "Read Holding registers."
DevAddress 256 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.R
EAD D ATA [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.
[+] Energy_Consumption REAL[1] Float