AT8xC51SND2C
Figure 49. Audio Output Format
Left Channel
Right Channel
DSEL
1
2
3
13
14
15
16
DCLK
DOUT
1
2
3
13
14
18
14
15
16
LSB MSB B14
B1 LSB MSB B14
I2S Format with DSIZ = 0 and JUST4:0 = 00001.
B1
Left Channel
Right Channel
DSEL
DCLK
DOUT
1
2
3
17
18
32
1
2
3
17
32
MSB B14
LSB
MSB B14
LSB
I2S Format with DSIZ = 1 and JUST4:0 = 00001.
Left Channel
Right Channel
DSEL
DCLK
DOUT
1
2
3
13
14
15
16
1
2
3
13
15
16
MSB B14
B1 LSB MSB B15
MSB/LSB Justified Format with DSIZ = 0 and JUST4:0 = 00000.
B1 LSB
Left Channel
16 17
Right Channel
16 17
DSEL
DCLK
DOUT
1
18
31
32
1
18
31
32
MSB B14
B1 LSB
MSB B14
B1 LSB
16-bit LSB Justified Format with DSIZ = 1 and JUST4:0 = 10000.
Left Channel
15 16
Right Channel
15 16
DSEL
DCLK
DOUT
1
30
31
32
1
30
31
32
B2
B1 LSB
B2
B1 LSB
MSB B16
MSB B16
18-bit LSB Justified Format with DSIZ = 1 and JUST4:0 = 01110.
The data converter receives its audio stream from 2 sources selected by the SRC bit in
AUDCON1 register. When cleared, the audio stream comes from the MP3 decoder (see
Section “MP3 Decoder”, page 62) for song playing. When set, the audio stream is com-
ing from the C51 core for voice or sound playing.
As soon as first audio data is input to the data converter, it enables the clock generator
for generating the bit and word clocks.
Audio Buffer
In voice or sound playing mode, the audio stream comes from the C51 core through an
audio buffer. The data is in 8-bit format and is sampled at 8 kHz. The audio buffer
adapts the sample format and rate. The sample format is extended to 16 bits by filling
the LSB to 00h. Rate is adapted to the DAC rate by duplicating the data using DUP1:0
bits in AUDCON1 register according to Table 85.
The audio buffer interfaces to the C51 core through three flags: the sample request flag
(SREQ in AUDSTA register), the under-run flag (UNDR in AUDSTA register) and the
busy flag (AUBUSY in AUDSTA register). SREQ and UNDR can generate an interrupt
request as explained in Section "Interrupt Request", page 76. The buffer size is 8 Bytes
large. SREQ is set when the samples number switches from 4 to 3 and reset when the
samples number switches from 4 to 5; UNDR is set when the buffer becomes empty sig-
naling that the audio interface ran out of samples; and AUBUSY is set when the buffer is
full.
75
4341D–MP3–04/05
ATMEL [ ATMEL ]
