3.1.2 Synchronization Methods
The transport interface also can apply the signal DVALIDIN, indicating
valid input data, to allow gaps between input bytes. To avoid cyclic buffer
overrun or underrun, the average data input rate, measured over the
programmed block length, must not differ from the nominal payload rate
of the generated QAM signal. The circular buffer inside the L64777
allows a maximum 64-byte compensation of the input stream.
Synchronizing the QAM modulator with an input pulse at SSTARTIN sets
the byte and block boundaries with this external pulse. The transport
interface can reinsert the programmed sync byte at the location defined
by the external pulse.
In both the internal and external modes, the transport interface can
program the block length and the value of the sync byte. The block length
must be less than 256 bytes.
After the L64777 achieves synchronization, it inserts the sync byte into
the modulated stream according to the programmed sync byte. This has
the advantage of eliminating any error in the input sync byte as long as
the modulator remains synchronized.
3.1.3 Transport Error Indicator Handling
The transport interface can either pass on a transport error indicator
(TEI) unchanged from the input transport stream, or it can force the TEI
to indicate an error with the ERRORIN signal. The L64777 observes the
forced signal during the sync byte input and ignores it for the rest of the
input packet.
3.2 Serial Control Interface
The L64777 uses a serial control interface to control and setup the
programmable parameters of the chip. This interface is a slave-type only,
connected to the same serial bus as the LSI Logic L64724.
3-2
Interfaces
ETC [ ETC ]
