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APPENDICES
MELSEC-A
(3)
Ignoring wrong data
When any station is not transmitting data, the send line is in the high
impedance state.
Thus, the send line may become unstable due to noise, causing a
computer to receive wrong data.
Since a parity error or aframing error may occur in this case, error data
must be ignored.
When using protocol 1 to 4, either ACK, NAK, or STX code is transmitted
first.
Therefore until an ACK, NAK, or STX code is received, other codes must
be ignored.
When a computer has a pull-up/down register, wrong data is not received.
When a computer does not have a pull-upldown register, insert a resis-
tance (4.7 KR 114W as a standard resistance value) to prevent a receive
of wrong data.
I
M
Computer
APP
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12
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