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a) Track Jumping
Track jumping is performed automatically by the servo
LSI upon receipt of the appropriate command from the
microcomputer.
The
present
microcomputer
is
programmed to use 1,4,10 & 32 track jump
commands
to achieve searching. The 32 track jump command may
be used in pairs (64
tracks) or triplets (100 track) as
required. In TEST MODE the 1,4,10,32 & 100 track jump
and carriage
move sequences may be observed by
selecting the appropriate mode.
Note that the number of tracks jumped is controlled by
setting an internal counter to half the total value and
then counting this down using the zero crossing edges
of TEC1. Once the counter is at zero, a brake pulse of
KICK
TIN
h
TEC |
T. BRAKE
'
EQUALIZER
fixed duration
is output to bring the lens to a halt;
allowing tracking to be closed and normal
play to
continue.
For a fixed period of time after a multi-track jump has
been performed, a "tracking brake" circuit is activated in
conjunction with a "gain-up" equalizer to ensure that
the servo achieves stabilization before entering normal
play.
Manual track search, in normal mode, uses a group of
single track jumps to achieve FWD/REV at approx. ten
times normal play speed.
The figures 21 & 22 show the timing charts for the
single-track jump and multi-track jump commands.
BRAKE
h=te =170uS
ON
OFF
'
GAIN UP
| GAIN NORMAL:
—_—
Se
NORMAL
T. SERVO
:
OPEN
:
=
|
|
CLOSED
Fig.21: SINGLE TRACK JUMP
TIN
h
TEC I
(10 TRACK)
[ee
GAIN UP
ae
=
ax
an
mw
60ms
NORMAL
ON
T. BRAKE
OFF
OPEN
SERVO
'
CLOSED
CIN
|
i
pt
2.8ms (4,10 TRACK
JUMP)
5.8ms (32 TRACK JUMP)
Fig.22 : MULTI TRACK JUMP
1-25
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