SAA2501 Datasheet, PDF (25/52 Pages) NXP Semiconductors – Digital Audio Broadcast DAB decoder

Philips Semiconductors
Digital Audio Broadcast (DAB) decoder
Preliminary specification
SAA2501
7.20.5 SAA2501 STATUS
The host can check the status of the SAA2501 by reading the one-byte status word. After writing the SAA2501 ‘read
status’ operational address, the status byte may be read an arbitrary number of times. If status is read more than once,
it is updated by the SAA2501 between the individual readings. The status flags of the SAA2501 have the definition as
shown in Table 17.
Table 17 Status flag definitions
7
DST2⁽¹⁾
6
DST1⁽¹⁾
5
DST0⁽¹⁾
4
undefined
3
undefined
2
undefined
1
INSYNC⁽²⁾⁽³⁾
0
L3RDY⁽⁴⁾
Notes
1. By interpreting DST2 to DST0, the host can synchronize to the input frame frequency, and also determine at which
moment which L3 data item is available to be read. The value of DST2 to DST0 is only valid if flag INSYNC is set.
a) DST2 is a modulo 2 frame counter, i.e. DST2 inverts at the moment the decoding of a new frame is started. DST2
enables to host to sample the decoding subprocess DST1 to DST0 less frequently, meanwhile enabling the host
to see if it missed a state.
b) DST1 and DST0 values are explained in Table 18.
2. INSYNC is synchronization indication:
a) INSYNC = 0; the SAA2501 is not synchronized to the input data.
b) INSYNC = 1; the SAA2501 is synchronized to the input data.
3. As indicated in Section 7.20.8, some of the readable data item bits only have significance if INSYNC = 1.
4. L3RDY is L3 interface ready indication:
a) L3RDY = 0; the L3 interface cannot perform a new item data transfer yet.
b) L3RDY = 1; the L3 interface is ready for the next item data transfer.
After a device reset, L3RDY is cleared and will only become set after writing the first L3 control byte to the SAA2501.
The value of L3RDY can be tested by polling signal L3DATA instead of transferring the whole status byte.
Table 18 Status bytes DST1 and DST0
DST1
0
0
1
1
DST0
0
1
0
1
FUNCTION
subprocess 0; reading Ancillary Data or decoding header
subprocess 1; decoding bit allocation or scale factor select information
subprocess 2; decoding scale factors
subprocess 3; decoding samples
The DST1 and DST0 values in general do not have a determined duration. However, subprocess 3 takes at least
1_{⁄2 a frame period when ISO/MPEG layer I data is decoded, and} 5_{⁄6 of a frame period when ISO/MPEG layer II data is}
decoded. Table 19 indicates the validity of the SAA2501 readable data items with respect to the decoding subprocess.
Reading of a data item in a period when it is not valid renders undefined data.
January 1995
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