Table of Contents
Advertisement
5.
HALF-DUPLEX COMMUNICATIONS USING THE RS-232C INTERFACE
MELSEC-A
(2)
AJ71C24 is set t o " non-priority
".
,
,Conti n ue
data send
7
External device
A
Data A
Data
(
,
I
-
SD (send data)
RS (send request)
L
CS (clear to send)
L
-
CD (receive carrier
detect)
C24 stores received
-
RD (received data)
The following steps describe the operations required for an external device at
every timing mentioned by (1) t o (6) i n the above figure.
The signal name is the signal of the AJ71C24.
As described in (I), turn ONIOFF the CD signal of the AJ71C24 with the
external device and do data transmission t o the AJ71C24.
(Note that 5) and 6) are different i n the non-priority setting.)
I
1)
When not transmitting data from the external device t o the
AJ71C24, turn the CD signal OFF.
2) When doing a data send, check the RS signal. If the RS signal is
OFF. turn the CD sianal ON.
lf the RS signal is 0 i , wait until it turns OFF. After the RS is turned
OFF, turn the CD signal ON.
3) After turning the CD signal ON, transmit data.
4) After completing the data send, turn OFF the CD signal.
5) Even if the RS signal turns ON during data transmission, continue
the data send to the AJ71C24. (This occurs when the AJ71C24
and the external device start data transmission simultaneously.)
6) After the send from the external device is completed, transmit data
from the AJ71C24 to the external device.
Section 5.4.2 gives details.
IREMARKJ
When (a) starting or during data transmission to the AJ71C24, and (b) if the DTR(ER) signal of
AJ71C24 turns
OFF,
interrupt data transmission until the DTR signal turns ON.
See Appendix 4.
Advertisement
Table of Contents
