Logix5000 Controllers General Instructions - SLAC Confluence

ASCII Serial Port Instructions (ABL, ACB, ACL, AHL, ARD, ARL, AWA, AWT) 579Description:The ACB instruction counts the characters in the buffer.To program the ACB instruction, follow these guidelines:1. Configure the serial port of the controller for user mode.2. 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.Arithmetic Status Flags:Fault Conditions:not affectednoneExecution:Condition Relay Ladder Action Structured Text Actionprescan The rung-condition-out is set to false. No action taken.rung-condition-in is false The rung-condition-out is set to false. narung-condition-in is true The instruction executes when rung-condition-intoggles from cleared to set.naThe rung-condition-out is set to true.EnableIn is set na EnableIn is always set.instruction executionThe instruction counts the characters in the buffer.The .EN bit is set.The remaining status bits, except .UL, are cleared.The instruction executes.The instruction attempts to enter the ASCII queue.postscan The rung-condition-out is set to false. No action taken.Example:Continuously count the characters in the buffer.Relay Ladderbar_code_count.EN/ACBASCII Chars in BufferChannel 0SerialPort Control bar_code_countCharacter Count 0ENDNERPublication 1756-RM003I-EN-P - January 2007