MT8979AP 데이터 시트보기 (PDF) - Zarlink Semiconductor Inc
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MT8979AP Datasheet PDF : 34 Pages
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MT8979
Data Sheet
Framing Algorithms
There are three distinct framers within the MT8979. These include a frame alignment signal framer, a multiframe
framer and a CRC framer. Figure 13 shows the state diagram of the framing algorithms. The dotted lines shows
optional features, which are enabled in the maintenance mode.
The frame synchronization circuit searches for the first frame alignment signal within the bit stream. Once
detected, the frame counters are set to find the non-frame alignment signal. If bit 2 of the non-frame alignment
signal is not one, a new search is initiated, else the framer will monitor for the frame alignment in the next frame. If
the frame alignment signal is found, the device immediately declares frame synchronization.
The multiframe synchronization algorithm is dependent upon the state of frame alignment framer. The multiframe
framer will not initiate a search for multiframe synchronization until frame sync is achieved. Multiframe
synchronization will be declared on the first occurrence of four consecutive zeros in the higher order quartet of
channel 16. Once multiframe synchronization is achieved, the framer will only go out of synchronization after
detection of two errors in the multiframe signal or loss of frame alignment synchronization.
The CRC synchronization algorithm is also dependent on the state of the frame alignment framer, but is
independent of the multiframe synchronization. The CRC framer will not initate a search for CRC framing signal
until frame alignment synchronization is achieved. Once frame alignment synchronization is acquired, the CRC
framer must find two framing signals in bit 1 of the non-frame alignment signal. Upon detection of the second CRC
framing signal the MT8979 will immediately go into CRC synchronization. When maintenance feature is enabled
(maint bit = 1) the CRC framer will force a complete reframe of the device if CRC frame synchronization is not found
within 8 ms or more than 914 CRC errors occur per second.
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