Logix5000 Controllers General Instructions - SLAC Confluence

592 ASCII Serial Port Instructions (ABL, ACB, ACL, AHL, ARD, ARL, AWA, AWT)members of the SERIAL_PORT_CONTROL structure, rather than byincluding the values in the operand list.SERIAL_PORT_CONTROL StructureMnemonic Data Type Description.EN BOOL The enable bit indicates that the instruction is enabled..EU BOOL The queue bit indicates that the instruction entered the ASCII queue..DN BOOL The done bit indicates when the instruction is done, but it is asynchronous to the logic scan..RN BOOL The run bit indicates that the instruction is executing..EM BOOL The empty bit indicates that the instruction is done, but it is synchronous to the logic scan..ER BOOL The error bit indicates when the instruction fails (errors)..FD BOOL The found bit does not apply to this instruction..LEN DINT The length indicates the maximum number of characters to move to the destination (that is,when to stop reading if no termination characters are found)..POS DINT The position displays the number of characters that were read..ERROR DINT The error contains a hexadecimal value that identifies the cause of an error.Description:The ARL instruction removes characters from the buffer and storesthem in the Destination as follows:• The ARL instruction continues to execute until it removes eitherthe:– first set of termination characters– specified number of characters (Serial Port Control Length)• While the ARL instruction is executing, no other ASCII serial portinstruction executes.To program the ARL instruction, follow these guidelines:1. Configure the serial port of the controller:a. Select User mode.b. Define the characters that serve as the termination characters.2. Use the results of an ABL instruction to trigger the ARLinstruction. This prevents the ARL instruction from holding upthe ASCII queue while it waits for the termination characters.3. This is a transitional instruction:• In relay ladder, toggle the rung-condition-in from cleared toset each time the instruction should execute.• In structured text, condition the instruction so that it onlyexecutes on a transition. See .Publication 1756-RM003I-EN-P - January 2007