Publication 1763-RM001C-EN-P - October 2009
ASCII Instructions 311
• When the instruction is encountered on a rung and there are from 1
to 15 instructions in the ASCII queue, the instruction is put into the
ASCII queue and is executed when the preceding instructions are
completed. If the ASCII queue is full, the instruction waits until the
next program scan to determine if it can enter the ASCII queue. The
controller continues executing other instructions while the ASCII
port control instruction is waiting to enter the queue.
Programming ASCII Instructions
When programming ASCII output instructions, always precede the ASCII
instruction with conditional logic that detects when new data needs to be
sent or, send data on a time interval. If sent on a time interval, use an
interval of 0.5 second or greater. Do not continuously generate streams of
ASCII data out of a communications port.
Protocol Overview
Using the Full ASCII Instruction Set
To use the full ASCII instruction set, the communication channel must be
configured for ASCII protocol, as described below.
See on page 535 for the ASCII parameters that you set via the Channel 0
configuration screens in your programming software. Configuration of the
two append characters for the AWA instruction can be found in the
General tab of Channel Configuration option in RSLogix 500.
Using ASCII Instructions with DFI Full-Duplex
However, you can use the AWA and AWT instructions with DF1
Full-Duplex protocol. This functionality is provided for backward
compatibility with the legacy devices which are configured for DF1
Full-Duplex protocol to receive ASCII data from a controller.
IMPORTANT
If ASCII write instructions execute continuously, you may
not be able to re-establish communications with RSLogix
500 when the controller is placed into the RUN mode.
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