Mitsubishi MELSEC LJ71C24, Руководство пользователя

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11 DATA COMMUNICATION USING THE BIDIRECTIONAL PROTOCOL
1) When the control code ENQ is received, the C24 starts data reception processing.
When the data specified by the data length is received, the C24 ends the reception
processing of that data.
When sum check is enabled in the switch setting of GX Works2, the C24 checks
whether the message is normal or abnormal using the sum check code received
immediately after the message and the sum check code calculated by internal
processing.
When sum check is disabled in the switch setting of GX Works2, messages are
not checked using the sum check codes.
2) If the message has normally been received, the reception data read request
(X3/XA) turns ON.
If an error has been detected when receiving the message, the C24 sends an
abnormal end response (NAK message) to the external device.
The reception data read request will not be sent to the CPU module.
(The reception abnormal detection (X4/XB) does not come on.)
3) Control data is stored in the device designated with the BIDIN instruction and then
the BIDIN instruction is executed.
Receive data is read from the receive area of the buffer memory.
4) When the BIDIN instruction has been executed, the C24 sends a normal end
response (ACK message) to the external device.