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.
Table 4: Other GPIO usage with STV0681
GPIO
2
4
6
7
Audio Record
No
No
Yes
No
No
No
No
Audio
Yes
Playback
Flashgun
Yes
No
No
Yes
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.
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