Panasonic KX-FT21RS - Manual (Page 121)

6.5.3. Read Position Sensor (PS2)
When a document is brought to the read position, the shelter plate passes the sensor light, the photo transistor becomes ON, and
the input signal of the CN2-3 pin (Operation) becomes a low level. When there is no document at the read position, the shelter plate
closes the sensor light, the photo transistor becomes OFF, and the input signal of the CN2-3 pin (Operation) becomes a high level.
(When checking this sensor, CN1-8 pin, 2pin becomes low level).
Operation Board
Photo transistor Signal (CN2-3 Pin)
Out of the Read Position OFF High level
At the Read Position ON Low level
6.5.4. Document Sensor (PS1)
When a document is set, the shelter plate closes the sensor light, the photo transistor becomes OFF, and the input signal of the
CN2-3 pin (Operation) becomes a high level. When there is no document, the shelter plate passes the sensor light, the photo
transistor becomes ON, and the input signal of the CN2-3 pin (Operation) becomes a low level.
(When checking this sensor, the CN1-8 pin, 3pin becomes a low level.)
Operation Board
Photo transistor Signal (CN2-3 Pin)
No document ON Low level
Set document OFF High level
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KX-FT21RS