STV0680 datasheet(25/63 Pages) STMICROELECTRONICS

25 / 63 page

Version 3.4

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STV0680B + VV6444/6410/6500

STV0680B hardware interfaces

With STV0680B-003, these pins are used, as detailed in

Table 6.

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

4.9.5

Audio record hardware interface (STV0680B-003 only)

The firmware implements a successive approximation A/D conversion by outputting successive

analogue levels through the DAC output, which are compared with the actual signal level (output

from the sensor microphone preamplifier), and the resultant 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 STV0680B firmware speed.

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

4.9.6

Audio playback hardware interface (STV0680B-003 only)

The firmware 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.

4.10

Flashgun hardware interface (STV0680B-003 only)

STV0680B-003 will revert to flashgun exposure when it detects GPIO2 is high. Ideally the hardware

should combine the two factors of (a) user intention (e.g. user switches on flashgun) and (b) charge

sensing (i.e. flash is charged up and ready to fire).

These two factors (a) and (b) are independent, since there may be a delay of several seconds

between switching on the flashgun charger, and the flashgun being able to fire. To revert to flashgun

exposure before the flashgun is completely charged up would cause very bad pictures to be taken

in low light conditions because there is no “low light” threshold when flashgun exposure is enabled,

since the camera expects a flash to fire. A suggested flashgun hardware interface is given in the

flashgun application note AN1312.

When flashgun exposure is enabled and the shutter button is pressed, a picture will be taken and

the flash trigger pin GPIO7 will be pulsed low at the correct point in time so that all lines of the

CMOS imager are exposed.

4.11

IR filter

An Infra-Red Blocking Filter is required to achieve correct colour response. The exact specification

for the IR filter characteristics are given in the reference design manual.

GPIO

Audio Record

Yes

Audio

Playback

Yes

Flashgun

Yes

Table 6 : Other GPIO usage with STV0680-003

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