MT312 QPSK Demodulator
6.1.2 Viterbi mode. Register 25 (R/W)
Def
hex
NAME
ADR
B7
B6
B5
B4
B3
B2
B1
B0
VIT MODE
25
AUT IQ
V IQ
SP
CR
7/8
CR
6/7
CR
5/6
CR
3/4
CR
2/3
CR
1/2
R/W
44
B7:
B6:
AUT IQ
Automatic IQ phaseHigh = Search for correct IQ phase.
Low = Use IQ phase setting in V IQ SP.
When this bit is set high, the Viterbi decoder will start with the IQ phase defined in V IQ SP and the
code rate defined in VIT MODE[5:0], to establish the correct IQ phase of the incoming signal. When
this is established, the V IQ SP bit will be set to that phase indication so that it can be read by
software for subsequent re-tuning to the same channel.
V IQ SP
Swap I and Q inputs to the Viterbi decoder to overcome
spectral inversion caused by the transmitter.
High = I-Q swap
Low = No I-Q swap
If the transmitted signal is known to be spectrally inverted then set this bit to 1. If the spectral inversion
status of the transmitted signal is not known, then after QPSK CT lock, try to achieve FEC lock with
this bit first at zero and then at one.
When AUT IQ is set high, this bit will indicate the IQ phase following successful channel acquisition.
In manual mode, when AUT IQ is set low, software is required to determine the spectrum phase and
control this bit externally.
B5:
B4:
B3:
B2:
B1:
B0:
CR 7/8
CR 6/7
CR 5/6
CR 3/4
CR 2/3
CR 1/2
High = Viterbi code rate 7/8.
High = Viterbi code rate 6/7.
High = Viterbi code rate 5/6.
High = Viterbi code rate 3/4.
High = Viterbi code rate 2/3.
High = Viterbi code rate 1/2.
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