Sharp SF-1014 Service Manual page 114

4. Operating section
(1) Outline
The operating circuit is composed of the key matrix circuit and the
display matrix circuit.
Key detection: Keys are detected with signal matrix of W0 (Q25) ∼
W7 (Q32) and KEY0 ∼ KEY2.
With W0 signal at LOW (GND) and W1 ∼ W7 at HIGH (open), the
level of KEY0 ∼ KEY2 is checked and "H" or "L" state of 4K, 2K and
3K in the key matrix is judged to judge ON/OFF.
For W1 ∼ W7, switching is made every 2 msec for judgement.
W0
W1
W2
W3
W4
W5
W6
W7
KEY0
KEY0
+5V2
CPU
LC7935
2m sec
4K-ON
4K-OFF
+5V1
KEY0
KEY1
KEY2
4K
W0 (Q25)
16m sec
12 – 11
2K 3K
HIGH
GND