APPENDIX
AP-8
Serial interface I/O circuit
1. Input/Output Port SENSOR1, 2, 3, L/R, PC IO (PI), EXTRA1
(Transmission rate is selectable between 4800 bps and 38.4 Kbps.)
Input（
（（
（RD - A, B）
））
）
RD-A
RD-B
240 ohm
470 ohm x2
GND isolated
lsolated IO device
LTC1535
Logical High: A-B>+0.2V logical Low: A-B<-0.2V
240 ohms can be neglected by jumper plug.
Output (TD - A, B)
TD-A
TD-B
470ohm x2
Logical High: A-B>+4.0V at i
o=100 mA logical Low: A-B>-4.0V at io=100 mA
i
o is normally limited less than 100 mA on this device.
This means load resister equal to more than 50 ohms.
GND isolated
LTC1535
lsolated IO device
i
o
2. Input/Output Port BEACON, EXTRA (maker’s option)
These two ports are simply used Opt-coupler to isolate I/F only on RD terminal.
TD is not isolated and needed isolation by receiver’s responsibility.
220 ohm
RD-A
RD-B
RS422A device
SN75C1168
Input current is about 17 mA in case of A-B=+5V.
logical high: A-B< about +2V logical Low: A-B> about +2V
TD-A
TD-B
GND not isolated
470 ohm x2
logical High: A-B>+0.2V logical Low: A-B<-0.2V
i
o
is normally limited less than 100 mA.
This means that load resister must be more than 50 ohms.
RS422A device
SN75C1168
i
o
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