Sharp SF-1120 User Manual
Page 134
2
Operation
•
When "td" (= 30msec) passes after the voltage reaches 4.25V by
turning on the power, the output is drive to HIGH.
"td" is set by the external capacitor (C106).
Block diagram
(12) Operation panel
1
General
•
The operation circuit is composed of the key matrix circuit and the
display matrix circuit.
Key detection: With the signal detected by Q1
∼
Q7 and KI0
∼
KI3
signal matrix at LOW (GND) and Q2
∼
Q7 at HIGH (open), the
level of KI 0
∼
KI3 is checked to judge whether key matrix 1, 2, and
3 are HIGH or LOW, judging on/off.
For Q2
∼
Q7, switching is made every 2msec to judge each of
them.
R1
R2
1.25V
+
-
-
Power
5µA
reference
GND
Delay capacity
Output
t
ta
ta
H
L
Output not constant
ta = 30m sec
t
4.25V
0.65V
Po
w
e
r v
o
lt
a
g
e
Ou
tp
u
t s
tat
e
KI0
KI1
KI2
3
2
1
Q4
M66313
+5V2
+5V1
CPU
TD62504
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