Mitsubishi MELSEC LJ71C24, User Manual

Page: 215 / 428

11 - 29 11 - 29
11 DATA COMMUNICATION USING THE BIDIRECTIONAL PROTOCOL
POINT
(1) Perform error processing according to the error code received immediately
after the NAK message at the device that received NAK as the response
message after data transmission.
Chapter 15 shows the error codes that are transmitted from the C24.
(2) If the C24 receives an NAK response while transmitting data to an external
device, it completes data transmission, then reads the NAK, perform abnormal
completion.
(3) If the C24 detects an error while receiving data, it ignores the receive data
corresponding to the data length.
If the data length is abnormal, the C24 ignores all the data up to the receive
message head data (ENQ, etc.) received thereafter.
(5) External device time-out check
When checking time-out up to reception of the response message at the external
device during data transmission from external device to the C24, make the time-
out time the time shown below, or longer.
(CPU module maximum scan time 2) + 100 ms
(6) External device framing error
When nothing is transmitted from the C24 to the external device though the RS-
422/485 interface, a framing error may be generated in the external device.
Make the external device skip the data up to transmission of the head data (ENQ,
NAK, etc.) of the message from the C24.
Before communicating data through the RS-422/485 interface, check C24
specifications given in Section 6.3.
(7) Data bit settings
When adding a sum check code to a message, set the data bits to 8 bits using the
Transmission Setting of the GX Works2.
For more details on the data bit settings, refer to Section 7.3.1.