MT352
1.19
De-scrambler
Data Sheet
The de-scrambler de-randomizes the Reed-Solomon decoded data by generating the exclusive-OR of this with a
pseudo-random bit sequence (PRBS). This outputs 188-byte MPEG transports packets. The TEI bit of the packet
header is set to indicate uncorrectable packets.
1.20
MPEG Transport Interface
MPEG data can be output in parallel or serial mode. The output clock frequency is automatically chosen to present
the MPEG data as uniformly spaced as possible to the transport processor. This frequency depends on the guard
ratio, constellation, hierarchy and code rate. There is also an option for the data to be extracted from the MT352
with a clock provided by the user.
2.0
Software control
Acquisition of an OFDM channel and frequency scan for OFDM channels are controlled by an on-chip state
machine, which minimizes the software requirement in the host processor. To acquire a channel, the host programs
the channel frequency in the MT352. The on-chip state machine then writes the frequency information to the tuner,
awaits tuner lock and acquires the OFDM channel to generate the transport stream. The controller can be made to
automatically search for every parameter in the OFDM signal, including spectral inversion status. Furthermore, this
controller will re-acquire the channel in the event of an interruption to the incoming signal.
To scan a frequency range, the host programs the start and end frequencies for the search as well as the step size,
which defaults to 8 MHz. The MT352 then automatically scans the frequency range by appropriately programming
the tuner and searching for OFDM signals. Once a channel has been located, the host is interrupted to read the
channel information from the MT352. Then MT352 continues the search. By default, only the channels which can
generate a reliable transport stream are reported, but there is also provision for locating very weak channels. The
frequency capture range of MT352 can be maximized to capture channels with frequency offsets without re-
programming the tuner, in both 2 K and 8 K modes.
The above approach to channel acquisition and scan has resulted in very fast acquisition and scan times whilst
minimizing software overhead in the host processor. Furthermore, all this functionality has very efficiently been
mapped into hardware to result in a device consuming less than 220 mW of power.
3.0
Interfaces
Figure 5 - Primary Interfaces
The MT352 interfaces to other parts of a terrestrial receiver system can be partitioned into three groups: the host
controller, the tuner and the MPEG decoder. One other pin, the Status output, is multi-functional and can directly
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Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
