MITSUBISHI ELECTRIC QJ71C24N - Manual (Page 154)

7 - 3 7 - 3
MELSEC-Q
7 DATA COMMUNICATIONS USING BIDIRECTIONAL PROTOCOL
1) When the control code ENQ is received, the Q series C24 starts data reception
processing.
When the data specified by the data length is received, the Q series C24 ends the
reception processing of that data.
If "Sum check" is set with GX Developer, the Q series 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.
If "No sum check" is set with GX Developer, messages are not checked using
the sum check codes.
2) If the message has normally been received, the reception data read request signal
(X3/XA) turns ON.
If an error has been detected when receiving the message, the Q series C24
sends an abnormal end response (NAK message) to the external device.
The reception data read request will not be sent to the PLC CPU.
(The reception abnormal detection signal (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 Q series C24 sends a normal
end response (ACK message) to the external device.