Rockwell Automation Publication 1756-RM003N-EN-P - October 2011 579
ASCII Serial Port Instructions (ABL, ACB, ACL, AHL, ARD, ARL, AWA, AWT) Chapter 17
Description The ABL instruction searches the buffer for the first set of termination
characters. If the instruction finds the termination characters, it does the
following:
· Sets the .FD bit.
· Counts the characters in the buffer up to and including the first set of
termination characters.
The Controller Properties dialog box, User Protocol tab, defines the ASCII
characters that the instruction considers as the termination characters.
Follow these guidelines to program the ABL instruction.
1. Configure the serial port of the controller for user mode and define the
characters that serve as the termination characters.
2. This is a transitional instruction.
· In relay ladder, toggle the rung-condition-in from cleared to set each
time the instruction should execute.
· In structured text, condition the instruction so that it executes only on a
transition.
Arithmetic Status Flags: Not affected
Fault Conditions: None
Execution:
Condition Relay Ladder Action Structured Text Action
Prescan The rung-condition-out is set to false. No action taken.
Rung-condition-in is false The rung-condition-out is set to false. N/A
Rung-condition-in is true The instruction executes when rung-condition-in toggles
from cleared to set.
The rung-condition-out is set to true.
N/A
EnableIn is set N/A EnableIn is always set.
The instruction executes.
Instruction execution The instruction counts the characters in the buffer.
The .EN bit is set.
The remaining status bits, except .UL, are cleared.
The instruction attempts to enter the ASCII queue.
Postscan The rung-condition-out is set to false. No action taken.
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