User Manual

VS1003
8 FUNCTIONAL DESCRIPTION
SM_STREAM activates VS1003’s stream mode. In this mode, data should be sent with as
even intervals as possible (and preferable with data blocks of less than 512 bytes), and VS1003
makes every attempt to keep its input buffer half full by changing its playback speed upto 5%.
For best quality sound, the average speed error should be within 0.5%, the bitrate should not
exceed 160 kbit/s and VBR should not be used. For details, see Application Notes for VS10XX.
This mode does not work with WMA files.
SM_DACT defines the active edge of data clock for SDI. When ’0’, data is read at the rising
edge, when ’1’, data is read at the falling edge.
When SM_SDIORD is clear, bytes on SDI are sent as a default MSb first. By setting SM_SDIORD,
the user may reverse the bit order for SDI, i.e. bit 0 is received first and bit 7 last. Bytes are,
however, still sent in the default order. This register bit has no effect on the SCI bus.
Setting SM_SDISHARE makes SCI and SDI share the same chip select, as explained in Chap-
ter 7.2, if also SM_SDINEW is set.
Setting SM_SDINEW will activate VS1002 native serial modes as described in Chapters 7.2.1 and 7.4.2.
Note, that this bit is set as a default when VS1003 is started up.
By activating SM_ADPCM and SM_RESET at the same time, the user will activate IMA ADPCM
recording mode. More information is available in the Application Notes for VS10XX.
If SM_ADPCM_HP is set at the same time as SM_ADPCM and SM_RESET, ADPCM mode
will start with a high-pass filter. This may help intelligibility of speech when there is lots of
background noise. The difference created to the ADPCM encoder frequency response is as
shown in Figure 17.
0 500 1000 1500 2000 2500 3000 3500 4000
−20
−15
−10
−5
0
5
VS1003 AD Converter with and Without HP Filter
Frequency / Hz
Amplitude / dB
No High−Pass
High−Pass
Figure 17: ADPCM Frequency Responses with 8kHz sample rate.
SM_LINE_IN is used to select the input for ADPCM recording. If ’0’, microphone input pins
MICP and MICN are used; if ’1’, LINEIN is used.
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