SAA2501 Datasheet, PDF (11/52 Pages) NXP Semiconductors – Digital Audio Broadcast DAB decoder

Philips Semiconductors
Digital Audio Broadcast (DAB) decoder
Preliminary specification
SAA2501
Table 3 Muted frames
CRC
MINIMUM NUMBER OF MUTED FRAMES
DURING SYNCHRONIZATION
FREE FORMAT BIT NON-FREE-FORMAT
RATE
BIT RATE
No CRC
2
1
CRC
1
0
Table 4 Defaults master input bit rate
FSCLKM
0
1
Note
1. X = don’t care.
FSCLK384
0
0
1
0
1
0
1
7.11 Master input bit rate selection
As explained in Section 7.10, the SAA2501 can be used to
alternate between two applications: one with the slave
input, and one with the master input. When using the
master input, the SAA2501 should fetch data with the
effective bit rate, but cannot know what the bit rate of the
input data is until it has established synchronization. To
overcome this paradox, the input requesting is done at the
last selected bit rate.
After a device reset, the master input bit rate selection
defaults to the value indicated in Table 4.
FSCLKIN
X⁽¹⁾
256 × 32 kHz
384 × 32 kHz
256 × 44.1 kHz
384 × 44.1 kHz
256 × 48 kHz
384 × 48 kHz
DEFAULT MASTER INPUT
BIT RATE (kbits/s)
384
278.64
384
417.96
When FSCLKM = 0, the default master input bit rate is
384 kbits/s. When FSCLKM = 1, the SAA2501 uses signal
FSCLKIN to derive the selected bit rate, but it has no
indication concerning the sample rate corresponding to
FSCLKIN. Therefore, a bit rate of 384 kbits/s is selected at
an assumed sample rate of 44.1 kHz; with other sample
rates, the bit rate changes proportionally.
The consequence is that while the SAA2501 synchronises
(e.g. after a device reset), the application must at least be
able to supply at the given default bit rate the required
number of frames plus one additional frame (because of
the random decoding start point in the input bitstream).
Buffers in the application must thus be chosen sufficiently
large to prevent under or overflows.
The speed with which input data is requested by the
master input is changed by the SAA2501 in each of the
following cases:
1. When input synchronization is established after
checking a number of frames and the bit rate index of
the newly decoded bitstream indicates a different bit
rate than that currently selected. In this event, the bit
rate is adapted to the newly decoded index.
2. When the active input interface is changed from the
master to the slave input, or the signal STOP is
activated; in these events input requesting stops.
3. When the active input interface is changed from the
slave to the master input, or the signal STOP is
deactivated; the bit rate is set to the last selected
master input bit rate (the last selected master input bit
rate is memorised while using the slave input).
In all other events (e.g. when the SAA2501 goes and stays
out of synchronization), the data requesting speed of the
master input is maintained.
7.12 Sample rate selection
When using the slave input, or when using the master
input with FSCLKM = 1, the application must know the
sample rate: FSCLKIN must be applied, which has a
frequency which is a multiple of the sample rate; the
(sample rate dependent) I²S timing signals SCK and WS
are generated from FSCLKIN. These configurations will
normally be used in applications with a fixed sample rate.
Should the sample rate change, then the SAA2501 must
be reset.
January 1995
11