Relay Ladder - Allen-Bradley Logix5000 Reference Manual

Chapter 17 ASCII Serial Port Instructions (ABL, ACB, ACL, AHL, ARD, ARL, AWA, AWT)
Arithmetic Status Flags:
Fault Conditions:
Condition
Prescan
Rung-condition-in is false
Rung-condition-in is true
EnableIn is set
Instruction execution
Postscan
bar_code_count.EN
/
Grtr Than or Eql (A>=B)
Source A bar_code_count.pos
Source B
592
4. To trigger a subsequent action when the instruction is done, examine the
EM bit.
Not affected
None
Execution:
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 removes characters from the buffer and stores them in the destination.
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.
Example:
A bar code reader sends bar codes to the serial port (channel 0) of the controller.
Each bar code contains 24 characters. To determine when the controller receives a
bar code, the ACB instruction continuously counts the characters in the buffer.
When the buffer contains at least 24 characters, the controller has received a bar
code. The ARD instruction moves the bar code to the DATA member of the
bag_bar_code tag, which is a string.

Relay Ladder

GEQ
0
24
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.
ACB
ASCII Chars in Buffer
Channel
SerialPort Control bar_code_count
Character Count
ARD
ASCII Read
Channel
Destination bag_bar_code
SerialPort Control bar_code_read
SerialPort Control Length
Characters Read
EN
0 DN
ER
0
EN
0
DN
''
ER
24
0