SAA7371GP Philips Semiconductors, SAA7371GP Datasheet - Page 28

• Manufacturer Part Number: SAA7371GP
• Description: Digital servo processor and Compact Disc decoder CD7
• Manufacturer: Philips Semiconductors

Philips Semiconductors
7.14.6
A defect detection circuit is incorporated into the
SAA7371. 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
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.
7.14.8
7.14.8.1
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 hi-level status
command. The 8 signals are as follows;
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
5. Radial error: during radial on-track, no new subcode
1998 Jul 06
handbook, full pagewidth
Digital servo processor and
Compact Disc decoder (CD7)
before previous subcode time, or more than 10 frames
later than previous subcode time.
frame occurs within time defined by playwatchtime
parameter. During radial jump, less than 4 tracks have
sat1
sat2
D
O
H
EFECT DETECTION
I
FF
Interrupt mechanism and STATUS pin
-
LEVEL FEATURES
-
TRACK DETECTION
DECIMATION
FILTER
Fig.20 Block diagram of defect detector.
FILTER
FAST
FILTER
SLOW
28
6. Autosequencer state change.
7. Autosequencer error.
8. Subcode interface blocked: the internal decoder
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
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).
7.14.8.3
Three watchdogs are present:
1. Focus: detects focus drop out of longer than 3 ms, sets
2. Radial play: started when radial servo is on-track
3. Radial jump: active when radial servo in long jump or
The focus watchdog is always active, the radial watchdogs
are selectable via the radcontrol parameter.
been crossed during time defined by jumpwatchtime
parameter.
interface is being used.
focus lost interrupt, switches off radial and sledge
servos, disables drive to disc motor.
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.
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.
GENERATION
Decoder interface
Automatic error handling
DEFECT
PROGRAMMABLE
HOLD-OFF
Product specification
SAA7371
MBG421
defect
output