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1998 Feb 16 16
Philips Semiconductors Product specification
CMOS digital decoding IC with RAM for
Compact Disc
SAA7345
Fig.13 Concealment mechanism.
Interpolation Hold Interpolation
MGA372
OK Error OK Error Error Error OK OK
MUTE,ATTENUATION AND FADE
A digital level controller is present on the SAA7345 which
performs the functions of soft mute, attenuation and fade.
Mute and Attenuation
Soft mute is activated by sending the Mute command to
the fade control register (address 0000, data X000). The
signal will reduced to zero in up to 128 steps (depending
on the current position of the fade control), taking a
maximum of 3 ms.
Attenuation (−12 dB) is activated by sending the Attenuate
command to the fade control register (data X01X).
Attenuation and mute are cancelled by sending the Full
Scale command to the fade control register (data X001). It
will take 3 ms to ramp the output from mute to the full-scale
level.
Fade
The audio output level is determined by the value of the
internal fade counter.
• The counter is preset to 128 by the Full Scale command
if no oversampling is required.
• The counter is preset to 120 (−0.5 dB scaling) by the Full
Scale command if either 2f
s
or 4f
s
oversampling is
programmed in the DAC output register (address 0011).
• The counter is preset to 32 by the Attenuate command.
• The counter is preset to 0 by the Mute command.
Level
counter
128
----------------------
maximum level×=
To control the fade counter in a continuous way, the
step-up and step-down commands are available (fade
control register data X101 and X100). They will increment
or decrement the counter by 1 for each register write
operation.
• When issuing more than 1 step-up or step-down
command in sequence, the write repeat mode may be
used (see Fig.6).
• A pause of at least 22 µs is necessary between any two
step-up or step-down commands.
• When a step-up command is given when the fade
counter is already at its full-scale value, the counter will
not increment.
DAC Interface
The SAA7345 is compatible with a wide range of
Digital-to-Analog Converters. Eleven formats are
supported and are shown in Table 5.
All formats are MSB first. f
s
is 44.1 kHz in single-speed
mode and 88.2 kHz in double-speed mode.