STV0681 datasheet(25/44 Pages) STMICROELECTRONICS

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STV0681

STV0681 Hardware Interfaces

4.8

Switches and LED’s

The GPIO lines on STV0681 have the following pre-defined functions, see

Section 2.2 for user

interface functionality.

MODE push button and SHUTTER push button: GPIO0 and GPIO1: both push button inputs have

internal de-bounce circuits, reducing the amount of hardware required externally. It is

recommended that labelling is used on the camera casing to help the user understand the

functioning of the 2-button interface.

4.8.1

Input to select between 50 and 60Hz flicker frequency: GPIO3

This allows for factory setting of the anti-flicker frequency, dependant on the final country of

destination. See also

Section 2.6. The polarity of this selection is detailed in the reference design.

4.8.2

LED indicator output: GPIO5

The LED output has an 8mA current sinking capability.

4.8.3

Other pins: GPIO2, 4, 6, 7

With STV0681, these pins are used, as detailed in

Table 4.

Their specific functions are detailed in the reference design and in the following documents

available from ST:

Audio: application note AN1310

Flashgun: application note AN1312

4.8.4

Audio Record Hardware interface

STV0681 implements the A/D conversion by outputting successive analogue levels (successive

approximation) through the DAC output, which are compared with the actual signal level (output

from the sensor microphone preamplifier), and the resulting high or low signal from the comparator

is read at GPIO4. The sampling frequency is 11kHz, and the successive approximation is done at 8

bits resolution per sample. It is not possible to speed up the sampling frequency due to the limitation

of STV0681 processing speed.

An actual hardware implementation is given in the audio application note AN1310.

4.8.5

Audio Playback Hardware interface

STV0681 outputs the desired signal level through the DAC output, which is amplified to the speaker

or headphone socket. GPIO6 is used to switch off the amplifier during periods of audio recording, to

prevent the successive approximation waveform from being heard during periods of recording, and

to reduce the power consumption and unwanted crackle through the speaker.

An actual hardware implementation is given in the audio application note AN1310.

Table 4: Other GPIO usage with STV0681

GPIO

Audio Record

Yes

Audio

Playback

Yes

Flashgun

Yes

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