SM5902AF datasheet(31/40 Pages) NPC

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NIPPON PRECISION CIRCUITS-31

SM5902AF

Digital audio interface

When the DIT flag is set to 1, the digital audio inter-

face output from pin DIT is enabled. The output

data structure is modulated using a preamble and

biphase mark encoding.

Figure 5. Frame format

Figure 6. Subframe format

Channel 2

Channel 1

Frame 0

Frame 191

Channel 2

Channel 1

Channel 2

Channel 1

Frame 1

Frame 0

Sub Frame

Start Block

Auxiliary

Preamble

(Sync Groupe)

Digital Audio Sample Data

03 47 8

27 28

Audio Sample Validity

User Bit Data

Audio Channel Status

Sub Frame Parity

Preamble

Channel coding

Leading symbol = 0

Leading symbol = 1

11101000

00010111

11100010

00011101

11100100

00011011

The SM5902AF starts with 0, so only the preamble patterns for leading symbol = 0 are used.

Preamble

The preamble is a particular bit pattern used to per-

form subframe and block synchronization and dis-

crimination, assigned to one of 4 time slot divisions

(0 to 3), comprising 8 continuous biphase modulat-

ed transfer rate status indicators.

There are 3 types of preamble. The leading pream-

ble pattern of all blocks is preamble pattern B,

which is then followed by preamble pattern M for

channel 1, and preamble pattern W for channel 2.

Digital audio sample data and auxiliary audio

The digital audio sample data is a 20-bit digitized

audio signal. Auxiliary audio data, on the other

hand, can be audio sample data of varying length.

The SM5902AF uses a 16-bit audio data structure

internally with audio data output bits 4 to 11 set to 0

and bits 12 to 27 output in LSB first format.

Audio sample validity

The validity flag is set to 0 when the digital audio

sample data is output correctly, or it is set to 1 if the

output is incorrect. It is also set to 1 if encoding

does not start when the device is operating in

forced mute, microcontroller forced mute, and

shockproof mode.

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