Structured Text; Serial_Port_Control Structure - Allen-Bradley Logix5000 Reference Manual

Chapter 17 ASCII Serial Port Instructions (ABL, ACB, ACL, AHL, ARD, ARL, AWA, AWT)
AHL(Channel,ANDMask,ORMask,
SerialPortControl);
Mnemonic Data Type
.EN BOOL
.EU BOOL
.DN BOOL
.RN BOOL
.EM BOOL
.ER BOOL
.FD BOOL
.POS DINT
.ERROR DINT
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Structured Text

The operands are the same as those for the relay ladder AHL instruction.
However, you specify the Channel Status value by accessing the .POS member of
the SERIAL_PORT_CONTROL structure, rather than by including the value
in the operand list.

SERIAL_PORT_CONTROL Structure

Description
The enable bit indicates that the instruction is enabled.
The queue bit indicates that the instruction entered the ASCII queue.
The done bit indicates when the instruction is done, but it is asynchronous to the logic scan.
The run bit indicates that the instruction is executing.
The empty bit indicates that the instruction is done, but it is synchronous to the logic scan.
The error bit indicates when the instruction fails (errors).
The found bit does not apply to this instruction.
The position stores the status of the control lines.
The error contains a hexadecimal value that identifies the cause of an error.
Rockwell Automation Publication 1756-RM003N-EN-P - October 2011