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6.4 Sending/Receiving Flag Operation
6.4.1 No Header (Start Code), Terminator (End Code) "CR":
The "reception done" flag, the "sending active" flag, the GPSEND instruction, and the
GPRECV instruction are related as follows:
Data received
from external
device
SCU
receive bu ffer
No. of bytes
received
Reception
done flag
X0
GPRECV
instruction
execution
GPSEND
instruction
execution
General-purpose
communication
Sending active flag
Y8
Transmitted
data
Receive bu ffer
specified using
GPRECV instruction
The COM port has eight reception buffers. The reception process is continued after the
reception done flag (X0) turns ON. The reception done flag (X0) does not turn OFF
immediately following the execution of GPRECV instruction. It will be turned off at the
beginning of the next scan or later.
After GPSEND instruction is executed, data transmission is started in several μs to several
tens of ms. For time before transmission is started, please refer to the communication cycle
time (SM208-SM210) using the system monitor function.
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C
A
B
CR
Stored
A
A
A
B
B
C
<1>
<2>
<3>
6.4 Sending/Receiving Flag Operation
D
D
Data can be received until eight
receive bu ffers are all filled up even
if the reception done flag is turned on.
<1>
1
2
3
A
B
C
E
F
D
D
E
E
F
<2>
<3>
After GPRECV instruction is
executed, reception done
flag turns off at the beginning
of next scan or later.
3
CR
No. of bytes received
G
D
E
F
G
<4>
ON
OFF
ON
OFF
ON
OFF
ON
OFF
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