9.
COMMUNICATIONS
IN
THE
NO-PROTOCOL
MODE
Y
MELSEC-A
9.3.2
Presautione
durlng data communication8
(1) Communications with the computer
in
multidrop link.
In
the 1 :n multi-
drop link, the data sent from the computer is received by each AJ71 C24.
The message must contain the objective PC CPU where the data is sent
and,
at
the same time,
it
is necessary
to
write the sequence program
that ignores the received data addressed to other stations.
r
I
I
I
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1
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(2) Conditions when the AJ71 C24 transmission sequence is initialized
The transmission sequence is initialized in the following cases:
0
When the power is turned ON, the PC CPU is reset by the reset switch,
.The AJ71C24 CD signal is turned OFF during RS-232C full-duplex
or the mode is switched
communications.
If
the CD signal is turned
OFF
during send or receive processing,
data being processed for transmission or the data stored in the
AJ7lC24 receive data storing
OS
area is cleared.
In
full-duplex communications, keep the CD signal ON.
The ON/OFF status of the CD signal is ignored
if
'CD terminal
check disabled.
is
set at 10BH of the buffer memory address.
(3)
NULL code transmission from the AJ71 C24
A
framing error might occur at the AJ71C24
if
nothing is sent from the
computer to the AJ71C24 via the RS-422 interface. In this case, the
AJ71 C24 sends
'OOH"
(NULL code) to the computer. This NULL code
should be ignored by the computer.
J
1
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a
.?
(4) Combined use with dedicated protocols
When data communications is executed
in
the no-protocol mode,
if
the
AJ71C24 mode setting switch (see Section 4.3.1) is placed in any
position from 1 to
8,
or any mode number from
1
to
8
is designated by
the mode switching function, data communications with the other inter-
face can be executed using the dedicated protocol.
Data communications cannot be executed by setting one interface to
the bidirectional mode and the other to the no-protocol mode.
9-4
1
Y
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