Audio, video output circuit: at present, MT1389 all integrates video D/A converter, MT1389E inside
integrates audio D/A converter, manufactures select according to their own needs.
Please refer to
circuit principle diagram and audio circuit explanation for details.
3.2.8 Reset circuit
1. Reset circuit is shown as in the following figure 3.2.8.1:
C273
102
D201
1N4148
R219
100K
R222
33R
5
6
U205C
HCU04
URST#
DV33
C271
105
R221
10K(DNS)
8
9
U205D
HCU04
R220
100R
C272
103
Figure 3.2.8.1 Reset circuit diagam
2. Working principle: after power on, voltage of DV33 increases to 3.3V fast, main chip power
supply is normal. Now, for C271, C272 voltage to ground cannot change suddenly to make non gate
input end of U205C (that is 74HCU04 TTL non gate IC pin 5) presents low electric potential, now reset
signal URST keeps in low level to perform reset acts to main chip. DV33 charges C271 through R219,
and charges C272 through R220 at the same time to make the non gate input end electric potential
increase slowly. When voltage in this place increases to 1.4V, reset signal URST changes into high level
from low level to fulfil reset acts.
After power off, voltage of DV33 decreases. According to decreased waveform, we can see that the
front segment deceases quickly, and back segment decreases slowly. In the decrease course of DV33,
non gate input end electric potential of U205C discharges together with DV33 through D201 diode
1N4148.
- 25 -
Содержание DV725SI
Страница 1: ...service manual DV725SI...
Страница 62: ...21 27M clock signal waveform diagram 22 Reset circuit waveform diagram URST Dv33 58...
Страница 95: ...5 1 7 Surface layer of DECODE SERVO Board 91...
Страница 96: ...5 1 8 Bottom layer of DECODE SERVO Board 92...