5.
HALF-DUPLEX COMMUNICATIONS
USING
THE RS232C INTERFACE
MELSEC-A
(2) AJ71 C24 is set to
'I
non-priority
'I.
Continue
dam
transmission
BcuLJHCHbrlbkorr
prlory,ddmbrm*.lql*b
*Npp(.d*hnth.cD
tuna
ON.
'
External
device
Data
C
AJ7lC24
c__
SD
(send dam)
RS
(send
request)
CS
(clear
to
send)
-
CD
(receive
carrier
detect)
RD
(received dam)
__.
t
(6)
The following steps describe the operations performed by AJ71C24 at every
thing. The signal names are of the signals of the AJ71 C24.
As
described in
(l),
turn ON/OFF the
RS
signal of the AJ71C24 and do data
transmission to the external device.
Note that
5)
is different.
When not transmitting data from the external device to the
AJ71 C24, turn the
RS
signal OFF.
When doing a data send, check the CD signal.
If
the CD signal is
OFF, turn the
RS
signal
ON.
If the CD signal is
ON,
wait until
it
turns OFF. After the CD is turned
OFF, turn
ON
the
RS
signal.
After turning the
RS
signal
ON,
transmit data.
After completing the data send, turn OFF the
RS
signal.
If the CD signal turns
ON
during data send, stop the data send.
Then, turn the
RS
signal OFF and perform data receive process-
ing. (This occurs when the AJ71 C24 and an external device start
data transmission simultaneously.)
After transmission from the external device is completed, resend
all data from the beginning, or transmit data remaining after the
send interruption
in
5).
Data set at buffer address 110H is not transmitted.
*2 Resend all data from the beginning, or transmit data remaining
after the send interruption according to the setting of buffer
address
11
1
H.
[REMARK]
When
DTWDSR
control is being executed.
When (a) starting
or
during the data transmission to the external device and
(b)
il
the
DSR(DR)
signal
of
A171
C24
turns
OFF,
interrupt data transmission until the
DSR
signal turns ON.
See section
3.5.2.
h-.
,f--
.Y
-
c
I
c
5-9
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