7 DATA COMMUNICATIONS USING BIDIRECTIONAL PROTOCOL
(2)Confirmation using the module and GX
1)Confirmation using the display LED
When the Q series C24 detects an error, including a transmission error, the ERR LED lights up. (See Chapter 10.)
2)Confirmation using GX
•The monitor function is used to check for errors. (See Sections 8.6.3 and 8.6.6.)
•The ERR LED is turned off with the ERR LED OFF function. (See Section 8.6.10.)
3)Confirming the error code
Use one of the following to confirm the error code.
•GX
•GX Developer buffer memory monitor function (monitors addresses 258H/268H)
(3)Handling of receive data when a reception error occurs
1)All of the receive data for which an error was detected is ignored and an response message indicating an abnormal completion (NAK message) is sent to the external device.
When an error is detected during message reception, the Q series C24 does not issue a reception data read request to the PLC CPU.
2)The receive area in the buffer memory will contain the data received normally just prior to the error occurrence. (Data will not be rewritten.)
7.1.5Receive data clear
Data communications using the bidirectional protocol must be performed after a response message is received in reply to the preceding data transmission.
If the Q series C24 detects an error while receiving data, it sends an NAK message (response message) to the external device after the data reception completion and ignores the data being received when the error was detected.
Therefore, the receive data does not have to be cleared.
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