SAA7824 Datasheet, PDF (35/89 Pages) NXP Semiconductors – CD audio decoder, digital servo and filterless DAC with integrated pre-amp and laser control (PhonIC)

Philips Semiconductors
CD audio decoder, digital servo and filterless
DAC with integrated pre-amp and laser control
Product specification
SAA7824
7.16.9.4 Automatic sequencers and timer interrupts
Two automatic sequencers are implemented (and must be
initialized after Power-on):
• Auto-start sequencer: controls the start-up of focus,
radial and motor
• Auto-stop sequencer: brakes the disc and shuts down
the servos.
When the automatic sequencers are not used it is possible
to generate timer interrupts, defined by the
time_parameter coefficient.
7.16.9.5 High-level status
The read high-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.
7.16.10 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 or
2.1168 MHz; controlled via the xtra_preset parameter.
An analog representation of the output signals can be
achieved by connecting a 1st-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. At all other times, when the
laser is switched off, the RA and FO pins output a 2 MHz
50% duty factor signal.
7.16.11 LASER INTERFACE
The laser diode pre-amplifier function is built into the
SAA7824 and is illustrated in Fig.24. The current can be
regulated, up to 120 mA in four steps ranging from 58% up
to full power. New shadow register A (bank 2) and new
shadow register 3 (bank 3) are used to select the step
values.
The voltage derived from the monitor diode is maintained
at a steady state by the laser drive circuitry, regulating the
current through the laser diode. The type of monitor diode
being used (150 mV or 180 mV) must be selected by new
shadow register 7 (bank 2) (reset state = 150 mV).
The laser can be switched on or off by the xtra_preset
parameter; it is automatically driven if the focus control
loop is active.
2003 Oct 01
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