MT312CSLASHCG datasheet(39/90 Pages) ZARLINK

39 / 90 page

QPSK Demodulator

MT312

The Viterbi decoder will search for a signal with the code rates selected by this register. If one code rate is

selected, the MT312 will search for a signal with only that code rate. If the code rate is unknown then all B5:0

may be set, when the MT312 will search all code rates. It is possible to choose the starting point for the code

rate search by setting a bit in VIT SETUP[B3:1] register (86). After searching for a signal with the initial code

rate, if no signal is found the search proceeds to the next higher code rate, see 69.

In the DSS mode the code rate is not speciﬁed using VIT MODE register. If any of the two DSS bits of

Conﬁguration Register (127) is set, then the code rates selected by the VIT MODE register are ignored. The

DSS code rate selection is carried out as described in section 1.1, see 10.

The result of the search is reported in the FEC STAT register (6), see 49.

6.1.3 QPSK Control. Register 26 (R/W)

B7:

Reserved

Must be set low.

B6:

Q IQ SP

Swap I and Q inputs before QPSK demodulation to overcome spectral inversion

caused by the receiver front-end, for example through the swapping I and Q wires on

the board.

High = I-Q swap

Low = No I-Q swap

B5:

Reserved

Must be set low.Q MANHigh = QPSK manual programming

B4:

Reserved

Must be set low.OP CALHigh = Output calculation disable

B3:

Reserved

Must be set low.FLD LKHigh = Use Frequency Lock Detector lock

B2:

AFC M

High = Use AFC mode, for low Symbol rates only, < 10MSym/s.

B1:

Reserved

Must be set low.

B0:

ROLL 20

High = Roll-off 0.20

Low = Roll-off 0.35

If any of the two DSS control bits of the Conﬁguration Register (127) is active (see section 1.1 10), then bit B0

(ROLL 20) is ignored and the matched ﬁlter root-raised-cosine roll-off factor is taken as 0.20. Hence bit only

allows the choice of roll-off in the DVB mode.

NAME

ADR

Def

hex

QPSK

CTRL

Reserved

IQ SP

Reserved Reserved Reserved

AFC

Reserved ROLL

R/W

MT312C/CG Datasheet(PDF) 39 Page - Zarlink Semiconductor Inc

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