SAA7372 Datasheet, PDF (28/60 Pages) NXP Semiconductors – Digital servo processor and Compact Disc decoder CD7

Philips Semiconductors
Digital servo processor and Compact Disc
decoder (CD7)
Product specification
SAA7372
7.14.6 DEFECT DETECTION
handbook, full pagewidth
+
sat1
−
sat2
DECIMATION
FILTER
FAST
FILTER
SLOW
FILTER
DEFECT
GENERATION
Fig.20 Block diagram of defect detector.
PROGRAMMABLE
HOLD-OFF
defect
output
MBG421
A defect detection circuit is incorporated into the
SAA7372. If a defect is detected, the radial and focus error
signals may be zeroed, resulting in better playability. The
defect detector can be switched off, applied only to focus
control or applied to both focus and radial controls under
software control (part of foc_parm1).
The defect detector (see Fig.20) has programmable set
points selectable by the parameter defect_parm.
7.14.7 OFF-TRACK DETECTION
During active radial tracking, off-track detection has been
realised by continuously monitoring the off-track counter
value. The off-track flag becomes valid whenever the
off-track counter value is not equal to zero. Depending on
the type of extended S-curve, the off-track counter is reset
after 0.75 extend or at the original track in the 2.25 track
extend mode.
been crossed during time defined by jumpwatchtime
parameter.
6. Autosequencer state change.
7. Autosequencer error.
8. Subcode interface blocked: the internal decoder
interface is being used.
It should be noted that if the STATUS pin output is selected
via register 2 and either the microcontroller writes a
different value to register 2 or the decoder interface is
enabled then the STATUS output will change.
7.14.8.2 Decoder interface
The decoder interface allows registers 0 to F to be
programmed and subcode Q-channel data to be read via
servo commands. The interface is enabled/disabled by the
preset latch command (and the xtra_preset parameter).
7.14.8 HIGH-LEVEL FEATURES
7.14.8.1 Interrupt mechanism and STATUS pin
The STATUS pin is an output which is active LOW, its
output is selected by register 7 to be either the status bit
(active LOW) selected by register 2 (only available in
4-wire bus mode) or the interrupt signal generated by the
servo part.
8 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 listed below:
1. Focus lost: drop out of longer than 3 ms.
2. Subcode ready.
3. Subcode absolute seconds changed.
4. Subcode discontinuity detected: new subcode time
before previous subcode time, or more than 10 frames
later than previous subcode time.
5. Radial error: during radial on-track, no new subcode
frame occurs within time defined by playwatchtime
parameter. During radial jump, less than 4 tracks have
7.14.8.3 Automatic error handling
Three watchdogs are present:
1. Focus: detects focus drop out of longer than 3 ms, sets
focus lost interrupt, switches off radial and sledge
servos, disables drive to disc motor.
2. Radial play: started when radial servo is on-track
mode and a first subcode frame is found. Detects
when maximum time between two subcode frames
exceeds time set by playwatchtime parameter; then
sets radial error interrupt, switches radial and sledge
servos off, puts disc motor in jump mode.
3. Radial jump: active when radial servo in long jump or
short jump modes. Detects when the off-track counter
value decreases by less than 4 tracks between two
readings (time interval set by jumpwatchtime
parameter); then sets 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.
1998 Feb 26
28