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2. SYSTEM CONFIGURATIONS
MELSEC-A
2.3.5
m :
n ratio of
external devices to PC CPUs
(1) The system configuration for a m : n (up t o 32 stations) ratio of external
devices (such as a computer) t o PC CPUs is shown in Fig. 2.6 below.
(Mode:
[ I , [ I , [ I )
in the figure indicates setting set with the mode setting
switch of an AJ71C24 (see Section 4.3.1).
*
Set all
AJ71C24s
to the same protocol.
RS-232C cable
Computer link module
RS-422 interface
135-422
cable
RS-422 interface
RS-422
cable
R5-422 interface
Maximum of 32 stations
3
(1) All the external devices and AJ71 C24 modules are connected to form
a multidrop link i n the above example which uses dedicated
protocols 1, 2, or 4. The multidrop link of the m
:
n ratio system
configuration cannot use dedicated protocol 3.
When multiple external devices and AJ71C24 modules are used to
form a multidrop link, the procedure to exercise the access right with
a specific station should be provided.
(2) When the mode setting is 5 to
8,
the RS-232C interface which is not
used for the multidrop link can be used for communications with a
computer, a printer, or a CRT in a no-protocol/bidirectional mode.
(3) To have the RS-232C communicate over a distance greater than 15
m (49.2 ft), use a modem or RS-232ClRS-422 converter between the
external device and the AJ71C24.
Fig.
2.6
System Configurations (V)
2 - 1 6
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