Samsung DVD-905, Service Manual

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Reference Information
Samsung Electronics 2-17
2-4 Signal control chip DIC1, DIC6 description
2-4-1 Outline
DIC1(TC90A19F) performs PLL(Phase Locked Loop), Sync detection, demodulation and error correction after
converting RF signal inputted at DVD regeneration into digital data.
DIC6(TC6804F) receives signal-processed data in DIC1 and releases digital copy protection.
TC90A19F uses external memory(4M DRAM) as buffer as well as for error correction and carries out variable bit
rate transfer function. VBR function uses the external buffer as buffer to absorb the difference of transfer rate
occurring because the transfer rate of disk playback is faster than data transfer rate demanded by MPEG
decoder(Video/Audio Signal Process Chip).
In case of general disk refresh, the memory is almost filled up periodically. It is because Write rate to memory
after disk playback and signal process is faster than Read rate of MPEG decoder. When the memory is filled,
the fact is reported by interrupt to main micom, which controls the servo and kicks back the pick-up to the
previous track after memorizing the last data read from disk until now. It takes some times to jump to the
previous track and return to the original position(jump location) again. The full memory will have an empty
space because MPEG decoder reads out data of memory.
When the memory has an empty space, where data can be processed and written and the pick-up correctly gets to
the original location(kick back location) again, it reads data again and avoids the interrupt of data read
previously.
The basic operation repeats to perform disk data read --> memory full --> move pick-up to previous track --> disk
data read --> memory full --> move pick-up to previous track as described above.