SAA7824 Datasheet, PDF (34/89 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
handbook, full pagewidth
+
sat1
−
sat2
DECIMATION
FILTER
FAST
FILTER
SLOW
FILTER
DEFECT
GENERATION
PROGRAMMABLE
HOLD-OFF
defect
output
MBG421
Fig.22 Block diagram of the defect detector.
7.16.9 HIGH-LEVEL FEATURES
7.16.9.1 Interrupt mechanism and STATUS pin
The STATUS pin is an output which can be configured by
decoder register 7 and new shadow register C (bank 3) for
one of three different modes of operation. These are:
• Output the interrupt signal generated by the servo part
(it should be noted that the selection of this mode will
override all other modes)
• Output the decoder status bit (active LOW) selected by
decoder register 2 (only available in 4-wire bus mode)
• Output DC offset information (it should be noted that this
mode is used in conjunction with the decoder status
mode; see Section 7.5).
Eight signals from the interrupt status register are
selectable from the servo part via the interrupt_mask
parameter. The interrupt is reset by sending the read
high-level status command. The 8 signals are as follows:
• Focus lost: dropout of longer than 3 ms
• Subcode ready
• Subcode absolute seconds changed
• Subcode discontinuity detected: new subcode time
before previous subcode time, or more than 10 frames
later than previous subcode time
• Radial error: during radial on-track, no new subcode
frame occurs within the time defined by the
‘playwatchtime’ parameter; during radial jump, less than
4 tracks have been crossed during the time defined by
the ‘jumpwatchtime’ parameter
• Autosequencer state change
• Autosequencer error
• Subcode interface blocked: the internal decoder
interface is being used.
It should be noted that if the STATUS pin is configured to
output decoder status information [decoder register
7 = XX10 and new shadow register C (bank 3) = X00X]
and either the microcontroller writes a different value to
decoder register 2 or the decoder interface is enabled then
the STATUS output will change.
7.16.9.2 Decoder interface
The decoder interface allows decoder and shadow
registers to be programmed and subcode Q-channel data
to be read via servo commands. The interface is enabled
or disabled by the preset latch command (and the
xtra_preset parameter).
7.16.9.3 Automatic error handling
Three Watchdogs are present:
• Focus: detects focus dropout of longer than 3 ms, sets
focus lost interrupt, switches off radial and sledge
servos and disables the drive-to-disc motor
• Radial play: started when radial servo is in on-track
mode and a first subcode frame is found; detects when
the maximum time between two subcode frames
exceeds the time set by the playwatchtime parameter; it
then sets the radial error interrupt, switches radial and
sledge servos off and puts the disc motor into jump
mode
• Radial jump: active when radial servo is in long jump or
short jump modes; detects when the off-track counter
value decreases by less than 4 tracks between two
readings (the time interval is set by the jumpwatchtime
parameter); it then sets the radial jump error, switches
radial and sledge servos off to cancel jump.
The focus Watchdog is always active, the radial
Watchdogs are selectable via the radcontrol parameter.
2003 Oct 01
34