2.
SYSTEM
CONFIGURATIONS
MELSEC-A
2.3.3
2
:
1
ratio
of
external
devices
to
8
PC
CPU
(1)
The system configuration for a
2
:
1
ratio of external devices (such as
a computer) to a
PC CPU
is shown
in
Fig.
2.4
below.
(Mode:
[
]
to
[
I)
in
the figure indicates the range
of
setting designated
with the mode setting switch of an
AJ71C24
(see Section
4.3.1).
(A
combination
of
two systems each
of
which has a
1
:
1
configuration.)
mm
1-
External
device
(such
as
a
corn
puter, printer,
CAT)
External
devii
(such as
a
corn
puter, printer,
CRT)
AJ71 C24
POINTS
I
(1)
One of the
two
interfaces
is
set to a dedicated protocol
1,
2, 3,
or
4.
The other is set to a
no-protocol/bidirectional
mode.
(2)
The use
of
the
RS-232C
and the
RS-422
interfaces differs in that the
RS-422
is used to connect long distances (up
to
500
m
(1640.5
ft))
and the
RS-232C
is used to connect short distances (maximum
of
15
m
(49.2
ft)).
(3)
To have
the
RS-232C
communicate over
a
distance greater than
15
m
(49.2
ft),
use a modem or
RS-232C/RS-422
converter between the
external device and the
AJ71 C24.
Y
a
i
I
c
c
I
Fig.
2.4
System Configurations
(Ill)
2- 10
L
L
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