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:
Type Code Cause
4 57 The AHL instruction failed to execute because the serial port
is set to no handshaking.
Condition
Prescan
Rung-condition-in is false
Rung-condition-in is true
EnableIn is set
Instruction execution
Postscan
get_control_line_status
588
3. 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
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 obtains the control line status and turns on or off DTR and RTS signals.
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:
When get_control_line_status becomes set, obtain the status of the control lines
of the serial port and store the status in the Channel Status operand. To view the
status of a specific control line, monitor the SerialPortControl tag and expand the
POS member.

Relay Ladder

Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Recovery Method
Either:
·Change the Control Line setting of the serial port.
·Delete the AHL instruction.
Structured Text Action
No action taken.
N/A
N/A
EnableIn is always set.
The instruction executes.
No action taken.
AHL
ASCII Handshake Lines
Channel
AND Mask
OR Mask
SerialPort Control
Channel Status(Decimal)
EN
0
0 DN
0 ER
serial_port
29