Datasheet

4341H–MP3–10/07

AT8xC51SND2C/MP3B

Table 14-2. Sample Duplication Factor

14.5 MP3 Buffer

In song playing mode, the audio stream comes from the MP3 decoder through a buffer. The

MP3 buffer is used to store the decoded MP3 data and interfaces to the decoder through a 16-

bit data input and data request signal. This signal asks for data when the buffer has enough

space to receive new data. Data request is conditioned by the DREQEN bit in AUDCON1 regis-

ter. When set, the buffer requests data to the MP3 decoder. When cleared no more data is

requested but data are output until the buffer is empty. This bit can be used to suspend the audio

generation (pause mode).

14.6 Interrupt Request

The audio interrupt request can be generated by 2 sources when in C51 audio mode: a sample

request when SREQ flag in AUDSTA register is set to logic 1, and an under-run condition when

UDRN flag in AUDSTA register is set to logic 1. Both sources can be enabled separately by

masking one of them using the MSREQ and MUDRN bits in AUDCON1 register. A global enable

of the audio interface is provided by setting the EAUD bit in IEN0 register.

The interrupt is requested each time one of the 2 sources is set to one. The source flags are

cleared by writing some data in the audio buffer through AUDDAT, but the global audio interrupt

flag is cleared by hardware when the interrupt service routine is executed.

Figure 14-5. Audio Interface Interrupt System

14.7 MP3 Song Playing

In MP3 song playing mode, the operations to do are to configure the PLL and the audio interface

according to the DAC selected. The audio clock is programmed to generate the 256·Fs or

384·Fs as explained in Section "Clock Generator", page 75. Figure 14-6 shows the configuration

flow of the audio interface when in MP3 song mode.

DUP1 DUP0 Factor

0 0 No sample duplication, DAC rate = 8 kHz (C51 rate).

0 1 One sample duplication, DAC rate = 16 kHz (2 x C51 rate).

1 0 2 samples duplication, DAC rate = 32 kHz (4 x C51 rate).

1 1 Three samples duplication, DAC rate = 48 kHz (6 x C51 rate).

SREQ

AUDSTA.7

Audio

Interrupt

Request

UDRN

AUDSTA.6

MSREQ

AUDCON1.5

EAUD

IEN0.6

MUDRN

AUDCON1.4