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9. COMMUNICATIONS IN THE NO-PROTOCOL MODE
MELSEC-A
9.3.2
Precautions during data communications
(1) Communications with the computer in multidrop link. In the 1:n multi-
drop link, the data sent from thecomputer is received by each AJ71C24.
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.
(Message example)
(2) Conditions when the AJ71C24 transmission sequence is initialized
STX
IWW
The transmission sequence is initialized in the following cases:
Power is turned ON or the PC CPU is reset by the reset switch.
.The AJ71C24 CD signal is turned OFF during RS-232C full-duplex
communications.
Space
l20W
If the CD signal is turned OFF during send or receive processing,
data being processed for transmission or the data stored in the
AJ71C24 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 AJ71C24
w o n
number
0
2
l30M
1
l32W
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
AJ71C24 sends "OOH" (NULL code) to the computer. This NULL code
should be ignored by the computer.
(4) Combined use with dedicated protocols
Data lengm
(Binavdats)
I
With the mode setting switch (see Section 4.3.1) of theAJ71C24 placed
in any position between "1" through "E", if data communication is
executed in the no-protocol mode, data communications can be ex-
ecuted using the dedicated protocol with the other interface.
Data communications cannot be executed by setting one interface to
the bidirectional mode and the other to the no-protocol mode.
Data
CR
(ODH)
LF
IOAH)
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