Rockwell Automation 1794-OF8IH FLEX Isolated Input/Output HART Analog Modules - Manual (Page 48)

Publication 1794-UM065B-EN-E - September 2010
36 1794-IF8IH and 1794-OF8IH Configuration
data being received is in. No matter what the format, two bit sets will always
convey correct information to the module. Both sets must match each other
for the module to accept the configuration and begin processing it for
operation. If the two sets do not match, the module will revert to the last valid
configuration (in case of original start-up this would be default configuration)
and set module Diagnostic Status to 2, configuration failure.
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 will
be Little Endian.
Since these modules are HART modules, and HART data is normally provided
in Big Endian format, the module will be 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.
For FLEX I/O and FLEX Ex I/O: The Logix scanner byte swaps on word
boundaries, based on the GSD configuration data for a FLEX transfer. The
FLEX adapter byte swaps on word boundaries, based on the GSD
configuration data.
The test shows this to be true, that is, 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 I/O 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 would read the data off the wire. The FLEX I/O module would
word swap 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 I/O backplane gets
byte swapped on word boundaries onto the wire, and ends up in big Endian
format in memory.