VV6501 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

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VV6501

VGA CMOS Color Image Sensor

STMicroelectronics 

Functional Description

Table 5: User programmable clock divider values

clk_div[3:0]

101X

110X

111X

divide by

12

14

16

VV6501

3.1.11 Exposure/gain control

The sensor does not contain any form of automatic exposure or gain control. To produce a correctly

exposed image, exposure and gain values must be calculated externally and written to the sensor

via the serial interface.

Exposure calculation

The exposure time for a pixel and the ADC range (therefore the gain) are programmable via the

serial interface. The explanation below assumes that the gain and exposure values are updated

together as part of a 5 byte serial interface auto-increment sequence.

Exposure time combines coarse, fine exposure, pixel rate also related to frame and line lengths, all

defined in Table 6.

Table 6: Definitions related to exposure

Frame length

Line length

Exposure

Coarse exposure

value

Fine exposure value

Pixel period

Exposure time

Number of lines per frame [default=524]

The frame length may be increased to 1023 by writing to the frame length register.

Number of pixels in a line [default = 762]

The line length may be increased to 1023 by writing to the line length register.

The pixel exposure time is determined by the course and fine exposure values

The number of lines a pixel exposes for.

Limited by frame length.

Coarse exposure value is in the range [0 - (frame length -2)].

Number of additional pixel periods a pixel exposes for.

Limited by line length.

Fine exposure value is in the range [11 - (line length)].

Determined by the input clock frequency (Fclkin) and user clk_div setting.

PixPeriod=(2*N)/Fclkin where N = clock divider ratio

PixPeriod x [(Coarsenum_lines x Line_Lengthnum_pixels) + Finepixels]

Example of exposure calculation in default VGA video mode

coarse exposure = 522

fine exposure = 762

Input clock frequency - Fclkin = 24MHz,

Pixel period = 2/(24 x 106) = 8.33 x10-8 s

Calculation: exposure time = 8.33 x10-8 x [(522 x 762) +762] = 33.2 ms

20/60

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