How To Read The Control Procedures Of The Mc Protocol - Mitsubishi MELSEC Q Series Reference Manual

2.3 How to Read the Control Procedures of the MC Protocol

External device side
Programmable
controller CPU side
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2 DATA COMMUNICATION USING THE MELSEC COMMUNICATION PROTOCOL
This section explains the control procedures when an external device accesses the
programmable controller CPU using the MC protocol.
(1) Transmission of command messages
Data communication through the MC protocol is performed using half-duplex
communication. ( 1)
When accessing the programmable controller CPU, send the next command
message after receiving a response message from the programmable controller
CPU side for the previous command message transmission.
(Command message)
1 When accessing via the C24, full-duplex communication is performed by
user setting when the on-demand function is being used.
When the system between external devices and programmable controller
CPUs is configured with a m:n connection, the next command message
transmission cannot be performed until data communication between either
of the external devices and programmable controller CPUs is completed.
(2) When a normal completion response message to a command
message cannot be received
(a) If an abnormal completion response message is received
Handle the case according to the error code in the response message.
(b) If the response message cannot be received or nothing can be received
• Via the E71
Send the command message again after the monitoring time of the
response monitor timer value has elapsed.
• Via the C24
Send the command message again after the monitoring time of the
response monitor timer (timer 1) has elapsed.
Modify the setting value of the monitoring time as needed.
In case of via the C24, try to modify the message wait time also.
(Response message)
(Command message)
(Response message)
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