CJ2 CPU Unit Software User's Manual - CIP ETI

10 CPU Unit FunctionsAdditional InformationThe internal logical ports in the CPU Unit are used both for background execution and the followinginstructions:• SEND(090), RECV(098), and CMND(490) (Network Instructions)• PMCR(260) (PROTOCOL MACRO)• TXDU(256) and RXDU(255) (the no-protocol communications instructions used with SerialCommunications Units)Background instructions and the above instructions cannot be executed simultaneously on thesame port. Use the Communications Port Enabled Flags to be sure that only one instruction isexecuted on each port at any one time.Note If an instruction is specified for execution in the background for a port for which the Communications PortEnabled Flag is OFF, the ER Flag will turn ON and the background instruction will not be executed. Communications Port Enabled FlagsThe Communications Port Enabled Flags are ON when the port is not being used and OFF whenprocessing is being performed on the port.10-2 Cycle Time/High-speedProcessing1010-2-5 Background ExecutionCommunications Port Enabled Flag10Background instruction processingfor user programInstructionexecutedCycle timeCycle timeCycle timeBackground executionI/O refreshCJ2 CPU Unit Software User’s Manual10-15