Instruction Execution - Allen-Bradley Logix5000 Reference Manual

ASCII Serial Port Instructions (ABL, ACB, ACL, AHL, ARD, ARL, AWA, AWT)

Instruction Execution

ASCII serial port instructions execute asynchronous to the scan of the logic.
Logic
Rung-condition-in of
instruction transitions
from false to true.
Instruction enters the
ASCII queue.
Serial Port
Each ASCII serial port instruction (except ACL) uses a
SERIAL_PORT_CONTROL structure to perform these functions:
· Control the execution of the instruction
· Provide status information about the instruction
The following timing diagram depicts the changes in the status bits as an ABL
instruction tests the buffer for termination characters.
Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
ASCII Queue
Instruction 1
Instruction 2
Instruction 3
Instruction 4
Data flows between
buffer and serial port.
Chapter 17
ASCII Task
Instruction at the top
of the queue executes.
Data flows
between task and
buffer.
Buffer
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