1766-RM001A-EN-P MicroLogix 1400 Programmable Controllers ...

306 Input and Output InstructionsAddressing Modes and File Types can be used as shown below:IOM Instruction Valid Addressing Modes and File TypesFor definitions of the terms used in this table see Using the Instruction Descriptions on page 92.Data FilesFunction FilesAddressModeAddress LevelParameterOISBT, C, RNFSTLMG, PDRI/RIXPLSRTCHSCPTOX, PWMXSTIEIIBHIMMILCDCS - CommsIOS - I/ODLS - Data LogImmediateDirectIndirectBitWordLong WordElementSlot • • • •Mask • • • • • • • • •Length•REF- I/O RefreshInstruction Type: outputREFExecution Time for the REF InstructionControllerMicroLogix 1400When Rung Is:TrueSee MicroLogix 1400 Scan TimeCalculation on page 550False0.1490 µsThe REF instruction is used to interrupt the program scan to execute theI/O scan and service communication portions of the operating cycle forall communication channels. This includes: write outputs, servicecommunications (all communication channels, communications togglefunctionality, and comms housekeeping), and read inputs.The REF instruction has no programming parameters. When it is evaluatedas true, the program scan is interrupted to execute the I/O scan andservice communication portions of the operating cycle. The scan thenresumes at the instruction following the REF instruction.The REF instruction cannot be executed from an STI subroutine, HSCsubroutine, EII subroutine, or a user fault subroutine.TIPUsing an REF instruction may result in input data changing in the middle ofa program scan. This condition needs to be evaluated when using the REFinstruction.ATTENTIONThe watchdog and scan timers are reset when executing the REFinstruction. You must insure that the REF instruction is not placed inside anon-terminating program loop. Do not place the REF instruction inside aprogram loop unless the program is thoroughly analyzed.Publication 1766-RM001A-EN-P - October 2008