Rockwell Automation 1769-ASCII Compact I/O ASCII Module - Manual (Page 83)

Rockwell Automation Publication 1769-UM012B-EN-P - January 2014 83
I/O Memory Mapping Chapter 3
Byte Swap Mode
To help with compatibility with end serial devices, the 1769-ASCII module
supports user-configurable options to byte swap data received from or
transmitted to the ASCII devices. Byte swapping of data is supported on 16- or
32-bit boundaries.
When Byte Swap mode is enabled, the user-defined Receive/Transmit Buffer
Length parameters must be evenly divisible by the bit boundary, 16- or 32-bit.
Transmit Serial ASCII Data
The Max Number of Transmit Characters parameter determines whether the
1769-ASCII module transmits data to a serial device.
If TX_String_Length = 0
The 1769-ASCII module receives data sent from the CompactBus Master and
uses the delimiter to determine how much data is sent to the serial device:
• If a transmit (or exclude) delimiter is in the string, all characters up to and
including the defined delimiter are sent to the ASCII device.
• If no delimiter is contained within the string, then the 1769-ASCII
module sends data received from the CompactBus Master to the ASCII
device.
If TX_String_Length > 0
The 1769-ASCII module receives data sent from the CompactBus Master
ignoring any embedded terminator. It sends the number of characters defined in
the Max Number of Transmit Chars parameter or the total sent by the Master,
whichever is less.
Receive ASCII Serial Data
The 1769-ASCII module receives and sends strings as defined in the Max
Number of Receive Characters parameter until the module receives a delimiter.
The 1769-ASCII module also sends the overflow error until a delimiter is
received. This process continues indefinitely until the ASCII device transmits the
specified delimiter.
IMPORTANT Byte Swap mode is valid only for nonzero length strings or non-character-
terminated data. It does not work with character-terminated strings when
the length byte is left at zero.
Termination characters are counted as part of the length of the nonzero
length strings.