Rockwell Automation 1794-OF8IH FLEX Isolated Input/Output HART Analog Modules - Manual (Page 74)

Publication 1794-UM065B-EN-E - September 2010
62 1794-IF8IH and 1794-OF8IH Configuration
for operation. If the two sets do not match the module reverts to the last valid
configuration (in case of original start-up this is the default configuration), set
module Diagnostic Status to "2" configuration failure, set outputs to fault
states and do not start operation.
Reasoning for this configuration parameter:
Within the CIP based Rockwell Automation (RA) control system all data is
transported and utilized in Little Endian format. As such the default mode of
operation for these modules is Little Endian.
Since these modules are HART modules, and HART data is normally provided
in Big Endian format, the module is responsible for converting any HART in
Big Endian format into Little Endian format.
Additionally, partners provide ProfiBus scanners and adapters for the RA
system. ProfiBus operates in Big Endian format.
The test shows this to be true, i.e. little Endian data from the FLEX backplane
gets byte swapped on word boundaries onto the wire, but ends up being back
in little Endian on Logix memory.
If a user utilized ProfiBus and Logix with these new FLEX I/O modules
having 32 bit REAL values he would leave the Byte Order parameter at
default. The Logix scanner byte swaps on word boundaries, based on the GSD
configuration data for a FLEX transfer. The FLEX I/O adapter byte swaps on
word boundaries, based on the GSD configuration data. True little Endian
REAL data from the FLEX backplane gets byte swapped on word boundaries
onto the wire, but ends up being back in little Endian on Logix memory.
If a user utilized ProfiBus with these new FLEX I/O modules having 32 bit
REAL values he would set the Byte Order parameter at Word Swap. The
scanner reads the data off the wire. The FLEX I/O module word swaps the
REAL values. The FLEX I/O adapter byte swaps on word boundaries, based
on the GSD configuration data. True little Endian REAL data from the
modules gets word swapped onto the FLEX backplane gets byte swapped on
word boundaries onto the wire, and ends up in big Endian format in memory.
Examples
In each of the following examples, the module operates internally with little
Endian byte order.