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10.
COMMUNICATIONS IN THE BIDIRECTIONAL MODE
MELSEC-A
10.3.3 Precautions during data communications
The conditions under which the AlSJ71C24 transmission sequence is
initialized are as follows:
The power supply is turned ON or the AlSCPU is reset with the reset
switch.
Data communications has completed normally.
.
The response message (ACK or NAK) is transmitted.
.
During full-duplex communications through the RS-232C interface, the
CD signal is turned OFF.
The ONIOFF status of the CD signal is ignored if the CD terminal
check function is disabled.
Send request signal made by the computer
a
To transmit data from an AlSJ71C24 send area to a computer receive
area, follow 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 (XnO) is turned ON.
When the send request signal is turned OFF by turning ON the send
completed signal, read the error code storage area (116H) for data
transmission to check the send result.
4
Data send from the computer send area or AlSJ71C24 send area
To transmit data from a computer or AlSJ71C24 in the bidirectional
mode, start data communications i n sequence only after the
receivelsend of the response for the previous data sendlreceive has
been completed.
Data length
The data length in a message must be smaller than the send or receive
data storage area that is set at the special applications area.
(a) Data transmitted from an AlSJ71C24 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 AlSJ71C24 receive
area
Data length must be smaller than the received data storage area
length [(set value at buffer memory address 107H)
-
1 (words)].
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