5.
HALF-DUPLEX COMMUNICATIONS USING THE
RS232C
INTERFACE
MELSEC-A
5.
HALF-DUPLEX COMMUNICATIONS
USING
THE RS232C INTERFACE
This section explains how to do half-duplex communications using an
RS-
232C interface to connect an external device and an AJ71C24.
This section does not apply to full-duplex communications.
AJ71 C24 can do half-duplex communications with an external device by using
the RS-232C interface by setting buffer memory.
While receiving data from en external device in half-duplex communications,
data is not transmitted from the AJ71C24 to the external device.
The key points for doing halfduplex communications between an external
device and the AJ71C24 using the RS-232C connector are as follows:
.System configurations and functions
.Buffer memory settings
.Wiring
.ON/OFF
timing of the CD and
RS
signals of the AJ71 C24
5.1
System Configuration8 and Functions
The following figure shows (a) the system configurations of the external device
and the PC CPU that can do half-duplex communications, and (b) the func-
tions of the AJ71 C24
Dodicatod Prolocol
No-protocoi
Yodo/Bidir.c-
tiorul Modo
I
Data
Data
Sond
from
tho
PC
Data Sond
CPU
by
tho
On-
and Data
demand
Function
Rocolvo
by a Command
Transmitled
from
PC
CW
tho Exiornai Dovico
\.
1:l
0
0.1
0
.2
1
:n
0
X X
*1 During data communicates, the send timing of data that a sequence
program requested to send changes due to the on-demand function.
See Section 8.14.2.
The send timing also changes as mentioned in *2 below.
*2 Send timing of data sent from the AJ71C24 and the external device
changes according to the set timing of "priorityhon-priority at the simul-
taneous transmission" set with the AJ71 C24.
See
Section 5.4.
1
i
1
5-1
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