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(3) Power: decode chip adopts twp groups power supply of 3.3V and 1.8V, in which 1.8V mainly
supply power for internal logic control circuit and we call it core voltage.
After power on, reset circuit performs reset to MT1389 built-in CPU (8032) and FLASH, decode chip
outputs reset signal at the same time and performs reset to other circuit. After system reset, it firstly
sends out read signal to FLASH to read out in formation saved in FLASH, the machine displays power-
on picture, servo system begins to work to check whether machine closes door to proper position and
whether detect switch has been closed, if not, the door close action is performed. After detect switch of
door is closed, the machine begins to perform preparations of disc reading and performs panel display
at the same time of working.
Playback process: laser head picks up disc signal from disc, after servo system processing, then
send to decode circuit for decoding, signal after being decoded is saved in SDRAM for the moment.
When machine needs to replay signal, decode circuit calls information inside SDRAM to perform D/A
conversion and then output.
User information storage: information content set by user is saved inside EEPROM, if user does not
refresh or reset this information, it will saved in IC permanently.
Audio, video output circuit: at present, MT1389 all integrates video D/A converter, MT1389HD
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
.
3.2.9 Reset circuit
1. Reset circuit is shown as in the following figure 3.2.9.1:
Figure 3.2.9.1 Reset circuit diagram