Specifications

17
AT83SND2CMP3
7524D–MP3–07/07
Clock Generator The audio interface clock is generated by division of the PLL clock. The division factor is
given by AUCD4:0 bits in CLKAUD register. Figure 14 shows the audio interface clock
generator and its calculation formula. The audio interface clock frequency depends on
the incoming MP3 frames and the audio DAC used.
Figure 14. Audio Clock Generator and Symbol
As soon as audio interface is enabled by setting AUDEN bit in AUDCON1 register, the
master clock generated by the PLL is output on the SCLK pin which is the DAC system
clock. This clock is output at 256 or 384 times the sampling frequency depending on the
DAC capabilities. HLR bit in AUDCON0 register must be set according to this rate for
properly generating the audio bit clock on the DCLK pin and the word selection clock on
the DSEL pin. These clocks are not generated when no data is available at the data
converter input.
For DAC compatibility, the bit clock frequency is programmable for outputting 16 bits or
32 bits per channel using the DSIZ bit in AUDCON0 register (see Section "Data Con-
verter", page 17), and the word selection signal is programmable for outputting left
channel on low or high level according to POL bit in AUDCON0 register as shown in
Figure 15.
Figure 15. DSEL Output Polarity
Data Converter The data converter block converts the audio stream input from the 16-bit parallel format
to a serial format. For accepting all PCM formats and I
2
S format, JUST4:0 bits in
AUDCON0 register are used to shift the data output point. As shown in Figure 16, these
bits allow MSB justification by setting JUST4:0 = 00000, LSB justification by setting
JUST4:0 = 10000, I
2
S Justification by setting JUST4:0 = 00001, and more than 16-bit
LSB justification by filling the low significant bits with logic 0.
AUCD4:0
AUDCLK
Audio Interface Clock
AUDclk
PLLclk
AUCD 1+
---------------------------=
Audio Clock Symbol
AUD
CLOCK
PLL
CLOCK
Left Channel Right Channel
POL = 1
POL = 0
Left Channel Right Channel