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 47 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 47. Audio Clock Generator and Symbol
AUDCLK
PLL
CLOCK
AUD
CLOCK
AUCD4:0
Audio Interface Clock
Audio Clock Symbol
PLLclk
AUCD + 1
AUDclk = ---------------------------
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 74), 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 48.
Figure 48. DSEL Output Polarity
Left Channel
Left Channel
Right Channel
Right Channel
POL = 0
POL = 1
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 I2S format, JUST4:0 bits in
AUDCON0 register are used to shift the data output point. As shown in Figure 49, these
bits allow MSB justification by setting JUST4:0 = 00000, LSB justification by setting
JUST4:0 = 10000, I2S Justification by setting JUST4:0 = 00001, and more than 16-bit
LSB justification by filling the low significant bits with logic 0.
74
AT8xC51SND2C
4341D–MP3–04/05
ATMEL [ ATMEL ]
