(7/8)
6. Reset Circuit
Figure 6.1 shows the reset circuit and its waveform. In this product, reset is cleared in about 100ms from the instant Vcc passes about
2.1V after having started from 0 V. When Vcc drops down to about 2.1V, reset turns effective.
Figure 6.1 Reset circuit and its waveform
By using SW5, the MCU can be reset manually.
Table 6.1 Function of SW5 (reset switch)
No. Name Function
SW5 RESET This is the reset switch. Press down this switch to reset the MCU.
R3
6.8K
C5
0.33uF
R4
10K
R5
10K
1
2
3
5
4
Vcc
IN OUT
Vss CD

M51957BL

SW4
IC3
MCU RESET
TP3
RESE T
td td

td = 0.34xCD(pF)usec

1.25V
H
L
Input volage
(IC3-2-pin
）
Output state
(IC3-5-pin）
ＣＤ
ｔ
ｔ

Detected power voltage (V)

Approx. 1.25x ( R3 + R4 )/ R4 Vcc