SAA7370 Datasheet, PDF (29/60 Pages) NXP Semiconductors – Digital servo processor and Compact Disc decoder CD7

Philips Semiconductors
Digital servo processor and
Compact Disc decoder (CD7)
Product specification
SAA7370
7.14.8.4 Automatic sequencers and timer interrupts
Two automatic sequencers are implemented (and must be
initialized after power-on);
1. Autostart sequencer: controls the start-up of focus,
radial and motor.
2. Autostop sequencer: brakes the disc and shuts down
servos.
When the automatic sequencers are not used it is possible
to generate timer interrupts, defined by the
time_parameter coefficient.
7.14.8.5 Hi-level status
The read hi-level status command can be used to obtain
the interrupt, decoder, autosequencer status registers and
the motor start time. Use of the read high-level status
command clears the interrupt status register, and
re-enables the subcode read via a servo command.
7.14.9 DRIVER INTERFACE
The control signals (pins RA, FO and SL) for the
mechanism actuators are pulse density modulated.
The modulating frequency can be set to either 1.0584 MHz
(DSD mode) or 2.1168 MHz; controlled via the xtra_preset
parameter. An analog representation of the output signals
can be achieved by connecting a first-order low-pass filter
to the outputs.
During reset (i.e. RESET pin is held LOW) the RA, FO and
SL pins are high-impedance.
7.14.10 LASER INTERFACE
The LDON pin (open-drain output) is used to switch the
laser off and on. When the laser is on the output is
high-impedance. The action of the LDON pin is controlled
by the xtra_preset parameter; the pin is automatically
driven if the focus control loop is active.
7.14.11 RADIAL SHOCK DETECTOR
The shock detector (see Fig.21) can be switched on during
normal track following, and detects within an adjustable
frequency whether disturbances in the radial spot position
relative to the track exceed an adjustable level (controlled
by shock_level). Every time the radial tracking error (RE)
exceeds this level the radial control bandwidth is switched
to twice its original bandwidth and the loop gain is
increased by a factor of 4.
The shock detection level is adjustable in 16 steps from
0 to 100% of the traverse radial amplitude which is sent to
an amplitude detection unit via an adjustable band-pass
filter (controlled by sledge_parm1); lower corner frequency
can be set at either 0 or 20 Hz, and upper corner
frequency at 750 or 1850 Hz. The shock detector is
switched off automatically during jump mode.
handbook, full pagewidth
RE
HIGH-PASS FILTER
(0 or 20 Hz)
LOW-PASS FILTER
(750 or 1850 Hz)
AMPLITUDE
DETECTION
SHOCK
OUTPUT
MGC914
1998 Feb 26
Fig.21 Block diagram of radial shock detector.
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