Rockwell Automation 1757-ABRIO Process Remote I/O (RIO) Communication Interface Module - Manual (Page 120)

118 Publication 1757-UM007D-EN-P - December 2008
Chapter 9 Accessing HART Data
Word 0
The \Program Files\1757AbRio\HartCmd directory contains files that
show the parameters required by each HART command and the data
returned by that command. For example, for command 1, read
primary variable, the file contains the following:
Cmd 01 Read Primary Variable from HART Device
Rsp
unit Primary Variable Unit
float Primary Variable
If either length is an odd number of bytes, round up to calculate
the number of words.
There are no parameters in the Cmd section, so in this case the
low byte, length to send, contains 7 + 0 = 7.
The high byte, expected reply length, contains 7 + 3 = 10 (5
bytes, rounded up to 3 words)
The Source Length in the MSG configuration dialog should be
set to match the length, in bytes, of the data to be sent. If the
length is 8 words, set the Source Length to 16.
Possible Types and Byte Counts
Type Byte Count
unit 1
byte 1
3bytes 3
float 4
date 3
text n where n < 4 and n < 64. The byte count is n * 3/4
TIP
If the command requires a float parameter, the value
must be reversed, byte by byte, before sending the data
on the HART network. Byte 0 becomes byte 3, byte 1
becomes byte 2, and so on. Similarly, if the reply data
contains a float, the bytes must be reversed.