ProSoft Technology MVI56E-MCMR - Manual (Page 74)

Configuring the MVI56E-MCMR Module MVI56E-MCMR ♦ ControlLogix Platform
User Manual Modbus Communication Module with Reduced Data Block
Page 74 of 225 ProSoft Technology, Inc.
May 13, 2014
2.3.7 Floating-Point Data Handling (Modbus Master)
In many applications, it is necessary to read or write floating-point data to the
slave device. The sample program only provides an INT array for the ReadData
and Write Data array (16-bit signed integer value). In order to read/write floating-
point data to and from the slave device, you must add additional ladder logic to
handle the conversion of the data to a REAL data type within the ControlLogix
processor. This is very easy to accomplish.
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.
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 Description
Enable = 1 Sends the command every time through the command list.
Internal Address = 1000 Places data at address 1000 of the module memory. Based on the
configuration in ModDef this will put the data at the tag
MCMR.DATA.R
EAD D ATA [0].
Poll Interval = 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 Modbus Slave Device Address 1.
Func = 3 Issues a Modbus Function Code 3 to "Read Holding registers."
MB Address in Device =
256 Along with the Function Code 3, MB Address in Device 256 will read
Modbus address 40257 of the Slave device.