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Reference:CMV300-datasheet-v2.11

CMV300 Datasheet

Page 26 of 54

5 IMAGE SENSOR PROGRAMMING

This section explains how the CMV300 can be programmed using the on-board sequencer registers.

5.1 EXPOSURE MODES

The exposure time can be programmed in two ways, externally or internally. Externally, the exposure time is defined as

the time between the rising edge of T_EXP1 and the rising edge of FRAME_REQ (see section 3.10 for more details).

Internally, the exposure time is set by uploading the desired value to the corresponding sequencer register.

The table below gives an overview of the registers involved in the exposure mode.

Exposure time settings

Default value

Description of the value

Exp_ext

41[0]

0: Exposure time is defined by the value uploaded in the

sequencer register (42-44)

1: Exposure time is defined by the pulses applied to the

T_EXP1 and FRAME_REQ pins.

Exp_time

42-44

488

When the Exp_ext register is set to ‘0’, the value in this

following formula: Exp_time x 325 x clk_per, where

clk_per is the period of the master input clock. The

minimal value for this is 1.

To calculate the exact exposure time when using internal exposure mode (Exp_ext = 0) use:

�� = ((

Exp_time − 1) ∗ 325 + [163 + (48 ∗ ��58)]) ∗ clk_per

Clk_per is the period of the input CLK_IN clock (or LVDS input clock divided by 12). The part [163 + (48*reg58)] should

always be a multiple of 325. So the “163” term depends on the value of reg58.

For external exposure mode (Exp_ext = 1) this becomes:

�� = Ext_exp_time + (48 ∗ reg58 ∗

clk_per)

Ext_exp_time is the time between the T_EXP1/2 and Frame_req pulses.

The 163 + (48 * reg58) or 48*reg58 is the part of the FOT for which the sensor is light sensitive (called exposure overlap)

and will therefore determine the minimum exposure time. Below you can see the detailed timing of one frame cycle in

internal exposure mode with Exp_time = 244, reg58 = 44, line time = 325*clk_per and clk_per is the period of the master

CLK_IN without multiplexing.

Frame_REQ

Frame_cycle

Exposure time

FOT

Actual exposure time = 251 * 325 * clk_per

244 * 325 * clk_per

Read-out time

13 * 325 * clk_per

7 * 325 * clk_per

Exposure overlap = min. exposure

FIGURE 30: FRAME CYCLE TIMING

We see that 163 + (48*reg58) = 7 * 325. So the exposure overlap during FOT is 7/13th of the total FOT.

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