Allen-Bradley Logix5000 Reference Manual page 579

Description
Arithmetic Status Flags:
Fault Conditions:
Execution:
Condition
Prescan
Rung-condition-in is false
Rung-condition-in is true
EnableIn is set
Instruction execution
Postscan
ASCII Serial Port Instructions (ABL, ACB, ACL, AHL, ARD, ARL, AWA, AWT)
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.
Not affected
None
Relay Ladder Action
The rung-condition-out is set to false.
The rung-condition-out is set to false.
The instruction executes when rung-condition-in toggles
from cleared to set.
The rung-condition-out is set to true.
N/A
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.
The rung-condition-out is set to false.
Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Structured Text Action
No action taken.
N/A
N/A
EnableIn is always set.
The instruction executes.
No action taken.
Chapter 17
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