VX6854LC datasheet(69/114 Pages) STMICROELECTRONICS

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VX6854LC

Video timing

6.5.2

Digital gain

To help compensate for the relatively coarse analogue gain steps, VX6854LC contains a

digital multiplier to “fill” in the missing steps. By mixing analogue and digital gain it is

possible to implement 3% gain steps across the full 1x to 16x gain range

The details of the digital gain implementation are:

•

four individual 16-bit digital channel gains (one per Bayer channel)

–

digital_gain_greenR (0x020E and 0x020F)

–

digital_gain_red (0x0210 and 0x0211)

–

digital_gain_blue (0x0212 and 0x0213)

–

digital_gain_greenB (0x0214 and 0x0215)

•

the digital gain range for each channel is 1.000 to 1.96875 in steps of 0.03125 (1/32),

that is, 5 fractional bits

–

digital_gain_min {0x1084:0x1085} = 0x0100 (1.00)

–

digital_gain_max {0x1086:0x1087} = 0x01F8 (1.96875)

–

digital_gain_step {0x1088:0x1089} = 0x0008 (0.03125)

6.5.3

Integration and gain parameter re-timing

The modification of exposure parameter (coarse, fine, clock division or gain) register values

does not take effect immediately.

The exact time at which changes to certain parameters take effect is controlled both to

ensure that each frame of image data produced has consistent settings and that changes in

groups of related parameters are synchronized.

To eliminate the possibility of the sensor array seeing only part of the new exposure and

gain setting, if the serial interface communications extends over a frame boundary, the

internal re-timing of exposure and gain data is disabled while writing data to the serial

interface register map. Thus if the 5 bytes of exposure and gain data is sent as an auto-

increment CCI sequence, it is not possible for the sensor to consume only part of the new

exposure and gain data.

However if it is not possible for the host to use auto-increment CCI register accesses and

only discrete register accesses are possible then the VX6854LC has a mechanism to

temporarily suspend the automatic application of updated exposure register values.

A group of parameter changes is marked by the host using a dedicated Boolean control

parameter, grouped_parameter_hold (register 0x0104). Any changes made to “retimed”

parameters while the grouped_parameter_hold signal is in the “hold” state will be

considered part of the same group. Only when the grouped_parameter_hold control signal

is moved back to the default “no-hold” state should the group of changes be executed.

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