Mitsubishi MELSEC-Q Series User Manual page 57

4 FUNCTIONS
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(2) Communication between the master and local stations by transient
transmission
Transient transmission sends and receives data in 1 : 1 mode by specifying the
opposite party at an arbitrary timing.
[Writing data to the buffer memory in a local station using the RIWT
instruction]
1) Data to be written to the buffer memory in a local station is stored in the
send buffer in the master module.
2) The data is written to the buffer memory in the local station.
3) The local station returns a writing complete response to the master
station.
4) The devices specified with the RIWT instruction are turned on.
Master station
PLC CPU
RIWT
Device memory
4)
[Reading data from the buffer memory in a local station using the
RIRD instruction]
1) The data in the buffer memory of the local station is accessed.
2) The data read is stored in the receive buffer of the master station.
3) The data is stored in the device memory of the PLC CPU and the
devices specified with the RIRD instruction are turned on.
Master station
PLC CPU
RIRD
Device memory
3)
POINT
Before performing data communication using transient transmission, the sizes of
the send and receive buffers must be set up in the buffer memory of the master
station. For more details on setting the sizes of the send and receive buffers, see
Section 6.2.
Master module
1)
Send buffer
Master module
Receive buffer
MELSEC-Q
Local station
2)
Buffer memory
3)
Local station
1)
Buffer memory
2)
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