IO.
COMMUNICATIONS
IN
THE
BIDIRECTIONAL
MODE
MELSEC-A
10.3.3
Precautionr, during
data
communlcrtknr
The conditions under which the AJflC24 transmission sequence is
initialized are as follows:
.The power supply is turned
ON,
the PC CPU is reset with the reset
0
Data communications
has
completed normally.
.The response message (ACK or NAK) is transmitted.
0
During full-duplex communications through the RS-232C interface,
the
CD
signal is turned
OFF.
The
ON/OFF
status of the CD signal
is
ignored if the
CD
terminal
check function is disabled.
switch, or
the
mode is switched.
1
Send request signal made by the computer
To transmit data from an AJ71C24 send area to a computer receive
area,
fdlow
the steps described in Section 10.9.
Once the send request signal (Y(n+l)O) is turned
ON,
do not turn
it
OFF
until the send completed signal @no)
is
turned
ON.
When the send request signal is turned
OFF
by turning
ON
the send
completed signal, read the error code storage area (1 16H) for data
transmission to check the send result.
Data send from the computer send area
or
AJ71C24 send area
To transmit data from a computer or AJ71 C24 in the bidirectional mode,
start data communications
in
sequence
only
after the receiveisend of
the response for the previous data sendireceive has been completed.
Data length
The data length in a message must be smaller thah the send or receive
data storage area that is set at the special applications area.
(a) Data transmitted from an AJ71 C24 send area to a computer-receive
area
Data length must be smaller than the send data storage area length
[(set value at buffer memory address 105H)
-
1 (words)].
(b) Data transmitted from
a
computer send area to AJ71C24 receive
area
Data length must be smaller than the received data storage area
length [(set value at buffer memory address 107H)
-
1 (words)].
10- 10
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