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10.
COMMUNICATIONS IN THE BIDIRECTIONAL MODE
MELSEC-A
10.1 Bidirectional Mode Basics
(1) What bidirectional mode means
In bidirectional communications:
The bidirectional receivebend area in an AJ71C24 buffer memory is
used for data commuications with a computer.
The data written to an AJ71C24 buffer memory by the TO instruction in
a sequence program is transmitted to a computer in the same code with
the control code (ENQ=05H) prefixed to the data to be transmitted.
(Sequence
buffer memory
program)
(00 H to FFH)
Bidirectional
I
C
I
Send request
signal ON
P C C P U
(Sequence
program)
Computer
"
1
code
K ,
'
I
An AJ71 C24 receives a response from a computer.
The data received from a computer is stored in an AJ71C24 received
area and read by the FROM instruction in the sequence program (the
data received is transferred in the code as received).
The resDonse data is transmitted to a computer in response to the read
compleied signal.
Read request
m
Bidirectional mode
(OOH
to
FFH)
receive area
(normab
E '
1
I
Data I
I
I
size I
r l I I
1
I
V
(abnormal)
Ignored
1
Error
'
I
N A
I
code
i
. ,
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