Prosoft-technology MVI69E-MBS Bedienungsanleitung PDF herunterladen (Seite 126)

Reference MVI69E-MBS ♦ CompactLogix Platform

User Manual Communication Module

Page 126 of 162 ProSoft Technology, Inc.

January 6, 2014

7.3.2 Configuring Floating-Point Data Transfer

A frequently asked question is how to handle floating-point data when the module

is used as a Modbus Master. This really depends on the slave device and how it

addresses this application.

Just because your application is reading or writing floating-point data, does not

mean that you must configure the Float Flag, Float Start, and Float Offset

parameters within the module.

These parameters are only used to support what is typically referred to as Enron

or Daniel Modbus, where one register address must have 32 bits, or one floating-

point value. Below is an example:

Example #1

Modbus Address

Data Type

Parameter

47101

32 bit REAL

TEMP Pump #1

47102

32 bit REAL

Pressure Pump #1

47103

32 bit REAL

TEMP Pump #2

47104

32 bit REAL

Pressure Pump #2

With the module configured as a Master, you only need to enable these

parameters to support a write to this type of addressing (Modbus FC 6 or 16).

If the slave device uses addressing as shown in Example #2, then you do not

need to do anything with the Float Flag or Float Start parameters, as this

addressing scheme uses two Modbus addresses to represent each floating-point

value:

Example #2

Modbus Address

Data Type

Parameter

47101

32 bit REAL

TEMP Pump #1

47103

32 bit REAL

Pressure Pump #1

47105

32 bit REAL

TEMP Pump #2

47107

32 bit REAL

Pressure Pump #2

Because each 32-bit REAL value is represented by two Modbus addresses

(example: 47101 and 47102 represent TEMP Pump #1), then you do not need to

set the Float Flag or Float Start for the module for Modbus FC 6 or 16 commands

being written to the slave.

The next few pages show three specific examples.

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