Mitsubishi MELSEC LJ71C24, User Manual

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11 DATA COMMUNICATION USING THE BIDIRECTIONAL PROTOCOL
(2) Confirmation using GX Works2, display unit and indicator LED of
C24
The following shows how to confirm the errors.
Item Reference
"Module's Detailed Information" screen Chapter 15
"Error History" screen Chapter 15
GX Works2
"Intelligent Function Module Monitor"
screen
GX Works2 Version1
Operating Manual
(Common)
Display unit Buffer memory monitor
MELSEC-L CPU Module
User's Manual (Function
Explanation, Program
Fundamentals)
Indicator LED of C24 ERR LED turns on Chapter 15
(3) Precautions
The following shows the precautions of receive data when a reception error
occurs.
1) All of the receive data for which an error was detected is ignored and a
response message indicating an abnormal completion (NAK message) is
sent to the external device.
If an error has been detected when receiving the message, the C24 does
not send the reception data read request to the CPU module.
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.)
11.1.5 Receive 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 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.