IO.
COMMUNICATIONS
IN
THE
BIDIRECTIONAL
MODE
MELSEC-A
10.8
Receiving
Data
In
the
Bidlractionrl
Modo
(Computer
-
AJtlC24)
(1) Data receive area
The AJ71C24 stores the received data length and the received data in
the data receive area.
With
a default setting,
80H
to
FFH
in
the buffer memory is allocated as
the data receive area.
This area may be changed as needed. Section 7.4.5 gives procedure
for changing the data receive area.
The unit
of
received data length
depends on the retting at address
103H
of
the word/byte setting area.
Received data length storage area
the data length in
the
received
message.
is
stored.
Received data storage area
Received data
is
stored
sequentially
from
the lowest address.
If
the length
of
the data area
in
the message transmitted from the
computer is greater than the received data storage area (default: 127
words), split the data area into several blocks
so
that its length
is
smaller than the received data storage area and append the block
number to specify each data area block.
Message format example:
I
I
E
sum
No.
I
kngth
Q
Block
Data
I
Data
Check
L,H
L
In
LIH;
Data
area
(2)
Reading received data
The AJ71C24 makes a read request to the
PC
CPU at the following
timing (the timing at which the XlAl signal
in
the program example
in
(4)
is turned on).
When the data length
in
the message and the set data length
(bytes
or
words as set
in
address
103H)
have been received.
If
the check sum is processed, when the check sum has been
received with the above mentioned data area.
Example:
Word/byte setting: Word units
Data length
in
message: 10
In
this case, the AJ71C24 makes a read request to the the
sequence program at the time 10 words
of
data (plus the check
sum) have been received.
m
u
I
',v
J
a
When the read request (Xnl) for the received data is made read the
data length and that length
of
data with a
FROM
instruction
in
a
sequence program and turn
OFF
the received data read completed
signal
(Y
(n+l)l).
'..-
7
id
10-20
1
i,
1
3
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