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2004 Jan 26 34
Philips Semiconductors Product specification
MPEG-2 video and MPEG-audio/AC-3
audio encoder with multiplexer
SAA6752HS
7.9 Clock generation
7.9.1 GENERAL
The SAA6752HS is designed to operate with a single
fundamental 27 MHz crystal or an external 27 MHz clock.
From these clock sources an internal PLL produces the
27 MHz, 54 MHz and 108 MHz frequencies needed for
operation.
It is possible to use a third overtone crystal in combination
with a 9 MHz external trap. In this event Clock mode 2 and
tuning by the I
2
C-bus commands are not usable.
7.9.2 CLOCK CONFIGURATION OPTIONS
The following configuration options can be selected from
the host:
• CLOCK MODE. Dependent on the type of application
(i.e. video frame locked, reference clock locked etc.),
three different clock modes are available
• CLOCK SOURCE. The clock can be generated from an
internal crystal controlled clock or an external source.
If from a crystal then a fine tune adjustment is available
• CLOCK OUTPUT. It is possible to enable a system clock
output so that the 27 MHz clock can be used elsewhere
by the user.
7.9.3 CLOCK MODES
The SAA6752HS internal PLL can be configured in three
different clock modes: Clock modes 1, 2 and 3. A definition
of the clock modes is shown in Table 9. The clock modes
are intended for different applications:
• Clock mode 1. System clock reference locked to input
video frame frequency. Intended for applications where
the output stream is recorded directly onto a medium
(i.e. DVD video recorder).
• Clock mode 2. Crystal locked to input video frame
frequency. Intended for applications that require both
recording and direct playback. However it is limited by
the required accuracy of the input video frame frequency
• Clock mode 3. Crystal free-running. Intended for
applications where the output stream is played real time
directly by a decoder.
To meet the requirements for each clock mode the
conditions specified in Table 10 must be met.
Table 9 Clock modes
Note
1. The stream contents are MPEG-compliant but the time stamps are not synchronized with real time (i.e. dependent
on the accuracy of the video input frame frequency). Playback of such a stream is MPEG-compliant due to the
re-generation of time synchronization.
Table 10 Clock modes requirements
Note
1. The nominal video frame frequency is dependent on the video mode set: 525 or 625 lines.
CLOCK
MODE
OUTPUT STREAM
TIME-STAMP COMPLIANCE
SYSTEM FREQUENCY SYSTEM CLOCK REFERENCE FREQUENCY
1 DVD-compliant
(1)
crystal frequency 27 MHz ± video frame frequency accuracy
2 DVD and MPEG-compliant 27 MHz ± video frame
frequency accuracy
27 MHz ± video frame frequency accuracy
3 MPEG-compliant crystal frequency crystal frequency
CLOCK
MODE
CRYSTAL FREQUENCY
EXTERNAL
CLOCK FREQUENCY
INPUT VIDEO FRAME FREQUENCY
(1)
1 27 MHz ±0.1% 27 MHz ±0.1% nominal − 8% to nominal + 2%
227× (1 ±200 × 10
−6
) MHz
(to allow fine tuning via PLL)
not applicable nominal × (1 ±200 × 10
−6
)
327× (1 ±30 × 10
−6
) MHz 27 × (1 ±30 × 10
−6
) MHz not applicable