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MELSEC-
A
6 EXCHANGING DATA WITH AN EXTERNAL DEVICE
6.4.2 Receiving data from an external device
The method for receiving data from an external device using the
transmission/reception buffer is explained in this section.
(1) Flow of process
The flow of the process for receiving data from an external device using the
transmission/reception buffer is shown below.
R2
RS-232-C
Master station
Bit device
Word device
Remote
input (RX)
Remote
output (RY)
Remote
output (RY)
Remote
input (RX)
7) Intelligent device
station access
complete ON
9) Intelligent device
station access
complete OFF
4) Intelligent device
station access
request ON
8) Intelligent device
station access
request OFF
Transmission
buffer
Reception
buffer
* When usin
g
the RIRD
(
RIRCV
)
command, the steps 4
)
to 9
)
are carried out automaticall
y
.
Programmable controller CPU
External
device
Trans-
mission
1) Data reception
Random data
3) Control data
5) Read command
2) Reception normal/
error read request
ON
12) Reception normal/
error read request
OFF
11) Reception read
complete ON
13) Reception read
complete OFF
10) Reception data
6) Control data +
reception data
OS reception
area
Reception
area