582 Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Chapter 17 ASCII Serial Port Instructions (ABL, ACB, ACL, AHL, ARD, ARL, AWA, AWT)
Description: The ACB instruction counts the characters in the buffer.
Follow these guidelines to program the ACB instruction.
1. Configure the serial port of the controller for user mode.
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:
Example:
Continuously count the characters in the buffer.
Relay Ladder
Structured Text
ACB(0,bar_code_count);
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.
/
bar_code_count.EN
EN
DN
ER
ASCII Chars in Buffer
Channel 0
SerialPort Control bar_code_count
Character Count 0
ACB
To Next Page
Loading...
Need help?
General
