FPΣCommunication Function 1 Computer Link8 - 48.1.2 Explanation of Operation when Using a Computer LinkCommand and ResponseInstructions pertaining to the PLC are called “commands”. These should be issued bythe computer, to the PLC.Messages sent back to the computer from the PLC are called “responses”. When thePLC receives a command, it processes the command regardless of the sequenceprogram, and sends a response back to the computer. The computer uses the responseto confirm the results of the command being executed.MEWTOCOL - COM sketchCommunication is carried out in a conversational format, based on the MEWTOCOL -COM communication procedures.Data is sent in ASCII format.The computer has the first right of transmission.The right of transmission shifts back and forth between the computer and PLC eachtime a message is sent.4 The unit number of the PLC thatsent the response5 Confirmation of whether or not theprocessing was carried out suc-cessfully6 The type of command processed7 If the command was used to readdata, the data that was read8 If an error occurred and the com-mand could not be processed suc-cessfully, the content of the errorCommand messages sent fromthe PLC should contain the follow-ing content:Command messages shouldcontain the following contentwhen sent:1 The unit number of the PLCto which the command isbeing sent2 The type of command3 Any settings and data re-quired in order to executethe commandComputerStartcodeCommand messageDestina-tion 1Text2 3CheckcodeEndcodeTransmission program Reception processing programThe command and data aresent to the PLC with thespecified unit number.A response is returned, and proc-essing is carried out based on thecontent of the response, such asretrieving any data that was sent.StartcodeSource4Text5 6 7 8CheckcodeEndcodeResponse messageFPΣFigure 141: FPΣ MEWTOCOL- COM
