MVI71-HART ♦ PLC Platform
Module Configuration
HART Multi-drop Master Communication Module
User Manual
Page 30 of 146
ProSoft Technology, Inc.
2.3.4 Hart Command Examples
This section describes two examples that shows how to configure HART commands.
The first example shows a read command (function code 3 - READ DYNAMIC
VARIABLES) and the second example shows a write command (function 34 - WRITE
DAMPING VALUE).
Example of HART Command Function 3
The following example shows how to configure a command function 3 (READ DYNAMIC
VARIABLES) to read the process variables from the HART slave device. According to
the HART specification, this command will return four floating-point variables:
Word
High Byte
Low Byte
0
Current (mA)
1
2
Primary Variable
3
4
Second Variable
5
6
Third Variable
7
8
Fourth Variable
9
The command also returns the following integer data:
Word
High Byte
Low Byte
0
Status Word
1
Primary Variable Units Code
Second Variable Units Code
2
Third Variable Units Code
Fourth Variable Units Code
So, this command will return the following number of words:
Parameter
Data Type
Direction
Number of
Words
Database
Address
(this example)
Variable Results
Floating Point
Read from slave to MVI
10
240 (word address)
Status/Unit Codes Integer
Read from slave to MVI
3
290 (word address)
The user can configure the command parameters as described in the following table in
order to correctly read the command 3 results to the module database:
Index
Parameter
Value
Observation
1
Enable
1
The command is sent continuously
2
Float DB
Address
240
The floating point results will be copied to the internal
database starting at word-address 240 (from 240 to
249)
3
Poll Interval
0
The command is sent without any delay
4
Word Count
10
The command returns 10 words of floating point data
5
Swap Code
3
The bytes in each returned floating point word are
swapped
