Philips CD721 - Page 27

3.4.2. Turntable motor control
The turntable motor speed is controlled by a fully integra-
ted digital servo. Address information from the internal +
8 frame FIFO and disc speed information are used to
calculate the motor contro/l output signals.
Several output modes are supported:
1. Pulse Density Modulation; 2-line(true complement
output), MHz sample frequency.
2. PWM output, 2-line, 22.05 kHz modulation frequency.
3. PWM output, 4-line, 22.05 kHz modulation frequency.
4. CDV motor mode.
The modes are selected via the motor output configurati-
on register.
In this application, the single-ended PDM mode is used.
In this mode, the motor output pin MOTO1 contains an
accelerating as well as a braking action.
50% duty cycle corresponds with the motor not actuated,
higher duty cycles mean acceleration, lower mean bra-
king.
Operation modes
The motor servo has the following operation modes
controlled by the motor mode register.
Start mode 1 Disc is accelerated by applying a positi-
ve voltage to the spindle motor. No
decisions are involved and the PLL is
reset. No disc speed information is
available for the microprocessor.
The disc is accelerated as in Start
mode 1, however th PLL will monitor
the disc speed. When the disc reaches
75% of its nominal speed, the controller
will switch to Jump mode.
Start mode 2
Jump mode Motor servo enabled but FIFO kept rest
at 50%. The audio is muted but it is
possible to read the subcode.
Similar to Jump mode but motor . inte-
grator is kept at zero. Used for long
jumps.
Jump mode 1
PCS 60 960
Play mode
Stop mode 1
Stop mode 2
Off mode
FIFO released after resetting to 50%.
Audio mute released.
Disc is braked by applying a negative
voltage to the motor. No decisions are
involved.
The disc is braked as in Stop mode 1,
but the PLL will monitor the disc speed.
As soon as the disc reaches 12% of its
nominal speed, the MOTSTOP status
signal will go HIGH and switch servo
to Off mode.
Motor is not steered.