SM5956A NPC, SM5956A Datasheet - Page 17

• Manufacturer Part Number: SM5956A
• Description: 6-channel Asynchronous Sample Rate Converter
• Manufacturer: NPC

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Digital Audio Interface
When the OEDITON pin is LOW, the digital audio interface output on DITO pin is enabled. The input signal
on DIA is sample rate converted, then a preamble is added and biphase mark encoded to form the output. In
through mode, the DITO pin is forcibly tied LOW-level. When the SM5956A is operating in slave mode, the
digital interface does not operate whenever the LRCO/BCKO are not operating as inputs.
Preamble
The preamble is a specific pattern used for subframe and block synchronization and discrimination. It is
assigned to the first four time slots (0 to 3) and is represented by 8 consecutive states when biphase mark
encoded at the transfer rate. There are 3 preamble patterns. The leading subframe within a block has a B pattern
preamble. All other channel 1 subframes have an M pattern preamble, and all channel 2 subframes have a W
pattern preamble.
Note. This LSI starts with a 0, therefore only the preamble for a 0 leading symbol is used.
Audio sample word and auxiliary data
The audio sample word is represented by 20 bits in the digitized audio signal. The auxiliary data has various
uses, including ancillary information or audio sample word length extension. The SM5956A audio data, how-
ever, is structured in 16-bit words, so bits 4 to 11 are output as 0 data. The audio data is output in bit positions
12 to 27 with the LSB first.
M Channel 1 W
Preamble
W
M
B
0
(Sync Group)
Preamble
Frame 191
3 4
Leading symbol: 0
Auxiliary
Channel 2
11101000
11100010
11100100
Channel coding
7 8
B
Sub Frame
Channel 1
Leading symbol: 1
Subframe Format
Audio Sample Word
Frame Format
00010111
00011101
00011011
SM5956A
Frame 0
Start Block
W
Sub Frame
Channel 2
Channel Status
Validity Flag
User Data
Parity Bit
M
27
Channel 1
SEIKO NPC CORPORATION —17
28
V
Frame 1
U
W
C
Channel 2
P
31