Mitsubishi MELSEC Q Series Reference Manual page 436

(2) When an external device writes data to the programmable
External
device side
Programmable controller CPU side
When the programmable controller CPU receives a command message from an
external device, it completes processing of the data in area A/C, then sends a
response message and waits for the next command message (neutral state).
6 - 3
controller CPU
(Command message)
1) Area C indicates transmission from the external device to the
programmable controller CPU.
2) Area B indicates transmission from the programmable controller CPU to
the external device.
3) The program of the external device is generated so that the data is
transmitted sequentially from left to right. (For example: in case of
area C, data should be sequentially sent from Header to the right.)
POINT
6 WHEN COMMUNICATING USING THE A COMPATIBLE 1E FRAMES
Area C
(Response message)
6 - 3