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
MV_line.EN
/
596
· In structured text, condition the instruction so that it executes only on a
transition.
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 the specified 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:
Continuously test the buffer for a message from a MessageView terminal. Since
each message ends in a carriage return ($r), the carriage return is configured as the
termination character in the Controller Properties
dialog box, User Protocol tab. When the ABL finds a carriage return, its sets the
FD bit.
When the ABL instruction finds the carriage return (MV_line.FD is set), the
controller has received a complete message. The ARL instruction removes the
characters from the buffer, up to and including the carriage return, and places
them in the DATA member of the MV_msg tag, which is a string.

Relay Ladder

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.
ABL
ASCII Test For Buffer Line
Channel
SerialPort Control MV_line
Character Count
EN
0 DN
ER
0