Table of Contents
Advertisement
5.
HALF-DUPLEX COMMUNICATIONS USING THE RS-232C INTERFACE
MELSEC-A
5.
HALF-DUPLEX COMMUNICATIONS USING THE RS-232C INTERFACE
This section explains how to do half-duplex communications using an RS-
2 3 2 6 interface to connect an external device and an AJ71C24.
I
This section does not apply to full-duplex communications.
I
AJ71C24 can do half-duplex communications with an external device by using
the RS-232C interface by setting buffer memory.
While receiving data from an external device in half-duplex communications,
data is not transmitted from the AJ71C24 to the external device.
The key points for doing half-duplex 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 AJ71C24
5.1
System Configurations and Functions
The following figure shows (a) the system configurations of the external device
and the PC CPU that can do half-dudex communications, and (b) the func-
tions of the AJ71C24
No-protocol
Dedicated Protocol
Modelbidirec.
tional
Mode
System
Data
Communications
Data
Send
the PC
by a Command
Data
Send
CPU by the
On-
and
Data
Transmitted
from
demand
Function
Receive
PC CPU)
the External
Device
o : Usable
x : Unusable
* I
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 "prioritylnon-priority at the simul-
taneous transmission" set with the AJ71C24.
See Section 5.4
Advertisement
Table of Contents
