2003 Oct 01 28
Philips Semiconductors Product specification
CD audio decoder, digital servo and filterless
DAC with integrated pre-amp and laser control
SAA7826
7.15.3 LOOP CHARACTERISTICS
The gain and crossover frequencies of the motor control
loop can be programmed via decoder registers 4 and 5.
The following parameter values are possible:
• Gains: 3.2, 4.0, 6.4, 8.0, 12.8, 16, 25.6 and 32
• Crossover frequency f
4
: 0.5 × n Hz, 0.7 × n Hz,
1.4 × n Hz and 2.8 × nHz
• Crossover frequency f
3
: 0.85 × n Hz, 1.71 × n Hz and
3.42 × n Hz.
It should be noted that the crossover frequencies f
3
and f
4
are scaled with the overspeed factor ‘n’ whereas the gains
are not.
7.15.4 FIFO OVERFLOW
If FIFO overflow occurs during Play mode (e.g. as a result
of motor rotational shock), the FIFO will be automatically
reset to 50% and the audio interpolator will conceal as
much as possible to minimize the effect of data loss.
Table 12 Operating modes
MODE DESCRIPTION
Start mode 1 The disc is accelerated by applying a positive voltage to the spindle motor. No decisions are
involved and the PLL is reset. No disc speed information is available for the microcontroller.
Start mode 2 The disc is accelerated as in start mode 1, however the PLL will monitor the disc speed. When the
disc reaches 75% of its nominal speed, the controller will switch to jump mode. The motor status
signals selectable via register 2 are valid.
Jump mode Motor servo enabled but FIFO kept reset at 50%, integrator is held. The audio is muted but it is
possible to read the subcode. It should be noted that in the CD-ROM modes the data, on EBU and
the I
2
S-bus, is not muted.
Jump mode 1 Similar to jump mode but motor integrator is kept at zero. It is used for long jumps where there is a
large change in disc speed.
Play mode FIFO released after resetting to 50% and the audio mute is released.
Stop mode 1 Disc is braked by applying a negative voltage to the motor; no decisions are involved.
Stop mode 2 The disc is braked as in stop mode 1 but the PLL will monitor the disc speed. As soon as the disc
reaches 12% (or 6%, depending on the programmed brake percentage, via register E) of its
nominal speed, the MOTSTOP status signal will go HIGH and switch the motor servo to off mode.
Off mode Motor not steered.
MGA362 - 2
G
f
4
fBW
3
f
Fig.20 Motor servo mode diagram.
