SAA7282 Datasheet, PDF (12/25 Pages) NXP Semiconductors – Terrestrial Digital Sound Decoder TDSD2

Philips Semiconductors
Terrestrial Digital Sound Decoder (TDSD2)
Product specification
SAA7282
Channel coding
Time-slots are encoded as biphase mark data. Each bit
transmitted is represented by a symbol comprising two
consecutive binary states. The first state of a symbol is
always different from the second state of the previous
symbol. The second state of the symbol is identical to the
first if the bit being transmitted is logic 0, however it is
different if the bit is logic 1 (see Table 7).
Preambles
Preambles are specific patterns providing synchronization
and identification of the sub-frames and blocks. A set of
three preambles is used. These preambles are transmitted
in the time allocated to four time-slots and are represented
by eight successive states. The first state of the preamble
is always different from the second state of the previous
symbol. Depending on this state the preambles are as
shown in Table 8.
Table 7 Channel coding.
Preceding state
Transmitted bit
0
1
0
1
Channel coding
11
00
10
01
Table 8 Preambles.
Preceding state
Preamble
B
M
W
0
1
Channel coding
11101000
00010111
11100010
00011101
11100100
00011011
The preambles preceding each digital audio sample are used to indicate the beginning of a sample as follows:
• Preamble B indicates the start of Channel A data and the beginning of a block
• Preamble M indicates the start of Channel A data but not the beginning of a block
• Preamble W indicates the start of Channel B data.
Channel status
The channel status information is organized in 192-bit words. The first bit of each word is carried in the frame with
Preamble B. The 192-bit word is organized into sections as shown in Table 9.
Table 9 Channel status codes.
BIT
0
1
2
3, 4
5
6, 7
8 to 15
16 to 19
20 to 23
24 to 27
28, 29
30 to 191
CODE
0
0
1
00
11
0
00
00110001
0000
0000
1100
00
all 0s
DESCRIPTION
consumer
sound data
digital copy permitted
indicates digital de-emphasis switched in
indicates digital de-emphasis switched out
category code
source code (don't care)
channel number (don't care)
sampling frequency (32 kHz)
clock accuracy (level II)
July 1993
12