SAA7282 Datasheet, PDF (11/25 Pages) NXP Semiconductors – Terrestrial Digital Sound Decoder TDSD2

Philips Semiconductors
Terrestrial Digital Sound Decoder (TDSD2)
Product specification
SAA7282
DIGITAL AUDIO INTERFACE IEC/EBU 958
Block structure
The output is grouped into a block of 192 consecutive
frames providing, for each channel the 192 channel status
data bits. The start of a block is designated by a special
sub-frame preamble.
Frame structure
Each frame is uniquely composed of two sub-frames. The
rate of transmission of frames corresponds exactly to the
source sampling frequency. In the 2-channel operation,
samples taken from both channels are transmitted by time
multiplexing in consecutive sub-frames. Sub-frames
related to Channel 1 (left or 'A' channel in stereophonic
operation and primary channel in monophonic operation)
normally use preamble M. However the preamble is
changed to preamble B once every 192 frames. This
defines the block structure used to organize the channel
status information. Sub-frames of Channel 2 (right or 'B'
channel in stereophonic operation and secondary channel
in monophonic operation) always use preamble W.
Sub-frame structure
Each frame is divided into 32 time-slots numbered 0 to 31.
Time-slots 0 to 3 carry one of three permitted preambles.
These are used to affect synchronization of sub-frames,
frames and blocks.
Time-slots 4 to 27 carry the audio sample word in linear
two's complement representation. The most significant bit
is carried by time-slot 27.
Time-slot 28 carries the validity flag associated with the
audio sample word. This flag is set to logic 0 if the audio
sample is reliable. If set to logic 1 then the sample is
unreliable.
Time-slot 29 carries one bit of the user data channel. In
this application this is not used and so is set to logic 0.
Time-slot 30 carries one bit of the channel status world
associated with the audio channel transmitted in the same
sub-frame.
Time-slot 31 carries a parity bit such that time-slots 4 to 31
inclusive will carry an even number of ones and an even
number of zeros.
handbook, full pagewidth
M channel 1 W channel 2 B channel 1 W channel 2 M channel 1 W channel 2
frame 191
sub-frame
sub-frame
frame 0
start of block
frame 1
MLB155
Fig.4 Frame format.
handbook, full pagewidth
0
34
11 12
L
sync
preamble
logical 0 bits
S
B
MLB156
audio sample word
27 28
31
M
S
B V UC P
validity flag
user data = logic 0
channel status
parity bit
Fig.5 Sub-frame format.
July 1993
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