VP310

PRELIMINARY DATA

18

2.2 Spectral Inversion

Spectral inversion of the QPSK signal can be caused by the transmitter or the receiver front-end.

In the latter case, this could happen due to the way I-Q conversion is carried out or because the I

and Q wires are swapped between the I-Q converter and the VP310. If spectral inversion is

caused by the receiver front-end, then this must be removed by swapping I and Q (within VP310)

before QPSK demodulation, by setting Q_IQ_SP bit B6 of QPSK_CTRL register (26) to 1.

If no spectral inversion is caused by the receiver front-end design, then bit B6 of QPSK_CTRL

must always be held at zero. If the transmitted signal is known to be spectrally inverted, then

V_IQ_SP bit B6 of the VIT_MODE register (25) must be set to 1. Then I and Q are swapped after

QPSK demodulation. If the spectral inversion status of the transmitted signal is not known, then

after QPSK has locked (i.e. QPSK_CT_LOCK = 1), the software must try to achieve FEC lock

with the bit B6 of VIT_MODE register first at zero and then at one.

2.3 Simple channel change sequence

If the VP310 is running, to change channel keeping the same signal conditions, it is only

necessary to change the tuner data and possibly the DiSEqC data. NO reset is necessary.

Program tuner via GPP in 'pass through mode'

open port with Reg 20 = 64 (40hex)

send TUNER DATA via I2C bus (5 bytes).

close port with Reg 20 = 0

DiSEqC mode

eg Vertical with 22kHz on:

Reg 22 = 1 (01hex)

GO

Re-acquire signal

Reg 27 = 1

Figure 14. Simple channel change sequence.