Rockwell Automation Publication 1756-RM003N-EN-P - October 2011 575
ASCII Serial Port Instructions (ABL, ACB, ACL, AHL, ARD, ARL, AWA, AWT) Chapter 17
Instruction Execution
ASCII serial port instructions execute asynchronous to the scan of the logic.
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.
Instruction enters the
ASCII queue.
ASCII Queue
Instruction 1
Instruction at the top
of the queue executes.
Buffer
Serial Port
Instruction 2
Instruction 3
Instruction 4
Rung-condition-in of
instruction transitions
from false to true.
Data flows
between task and
buffer.
Data flows between
buffer and serial port.
Logic ASCII Task
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