SAA2501 Datasheet, PDF (14/52 Pages) NXP Semiconductors – Digital Audio Broadcast DAB decoder

Philips Semiconductors
Digital Audio Broadcast (DAB) decoder
Preliminary specification
SAA2501
7.16 Decoding control signals
The decoding is performed by 3 signals as shown in
Table 6.
Table 6 Signals for decoding control
SIGNAL DIRECTION
FUNCTION⁽¹⁾
RESET
STOP
URDA
input
input
reset SAA2501 to
default state
stop decoding
unreliable input data;
interrupt decoding
The master reset signal RESET forces the SAA2501 into
its default state when HIGH. RESET must stay HIGH
during at least 24 MCLKIN periods if MCLKIN has
frequency of 24 MHz (i.e. MCLK24 = 1) or 12 MCLKIN
periods if MCLKIN has a frequency of 12 MHz
(MCLK24 = 0). At a reset, the SAA2501 synchronization to
the input bitstream is lost, the sub-band filter and
baseband audio output signals are muted, and the
SAA2501 settings are initialized.
The decoding can be stopped by making input signal
STOP HIGH. Stopping the decoding forces the SAA2501
to end decoding of input data, yet feeding zeroed
sub-band samples to the synthesis sub-band filter bank to
create a soft muting. When using the master input, input
requesting is also stopped. CDMWS stays in its current
state while STOP is asserted. The SAA2501 assumes the
input synchronization to be lost when the decoding is
stopped, thus causing re-synchronization when STOP is
de-activated again. Then the SAA2501 mutes, meanwhile
searching for a frame sync pattern or frame sync pulse (the
synchronization mode is selected via the L3 control bus) at
the input.
If synchronization is found, the SAA2501 starts producing
output data. The maximum response time to the activation
of signal STOP is half a sample period; the
re-synchronization time after STOP going LOW again
differs in various situations.
An ‘unreliable data’ indication can be given to the
SAA2501 by making signal URDA HIGH. URDA, like
STOP, mutes the sub-band signals and forces the
SAA2501 out of synchronization. However, in contrast to
STOP, master input data requesting continues at the bit
rate that was decoded before URDA became active. The
maximum response time to URDA is half a sample period.
7.17 Coded data interfaces
The SAA2501 contains:
• A coded data master input interface
• A coded data slave input interface (designed for EU147
format).
7.17.1 THE CODED DATA MASTER INPUT INTERFACE
When using the master input, the SAA2501 requests for
input data. With the master input, the coded input data may
not use the ISO/MPEG free format bit rate or be in EU147
format. The coded data master input interface consists of
4 signals (see Fig.7).
January 1995
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