Start Code "Stx", End Code "Etx - Panasonic FP7 User Manual

 After GPSEND command is executed, dual sending to the same port is not possible until the
"sending general-purpose communication flag" (Y8, Y9, YA) turns OFF. The "sending
general-purpose communication flag" (Y8, Y9, YA) turns OFF in command execution in the
next scan or later following completion of data sending.

7.5.2 Start Code "STX", End Code "ETX":

Receiving process: Reception done flag and GPRECV command are related as follows:
Data received
from external
device
SCU
receive bu ffer
No. of bytes
<1>
received
Reception
done flag
X0, X1, X2
GPSEND
instruction
execution
Receive bu ffer
specified using
GPRECV instruction
 When the start code is set to "STX", the data are saved in the reception buffer. When the
start code is received, the receive pointer is initialized. If there are two headers, data
following the second header overwrites the data in the reception buffer.
 The built-in SCU of the CPU unit has eight reception buffers. The reception process is
continued after the reception done flag (X0, X1, X2) turns ON. The reception done flag (X0,
X1, X2) does not turn OFF immediately following the execution of GPRECV command. It will
be turned off at the beginning of the next scan or later.

If there are no received data following execution of GPRECV command, the reception done
copy flag (X4, X5, X6) turns OFF.
KEY POINTS

The data without the Code STX at the reception is saved in the reception
buffer, and the "reception done" flag turns on when the end code is received.
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A B C STX
Stored
A A A A
B B B
C C
<2> <3> <0> <1>
Upon reception of the
start code, the reception
pointer is initialized.
7.5 Sending/Receiving Flag Operation
D E ETX F
D D D
F
B E E
Even in a
C C C
"reception done"
status, received
data is continued
into another
buffer, because
there are 4,096 x
8 reception
<2> <2> <1>
buffers.
No. of bytes received
2
D
E
G STX H ETX
F F H H
G G G G
<2>
<0> <1> <1>
Upon reception of the
start code, the reception
pointer is initialized.
7-15
ON
OFF
ON
OFF