CMV2000 datasheet(20/64 Pages) AMSCO

20 / 64 page

Reference: CMV2000-datasheet-v3.8

CMV2000 v3 Datasheet

Page 19 of 63

3.9.2 SPI READ

The timing to read data from the registers over the SPI interface can be found below.

SPI_EN

SPI_IN

SPI_CLK

C=’0'

SPI_OUT

½ CLK

1 CLK

FIGURE 12: SPI READ TIMING

To indicate a read action over the SPI interface, the control bit on the SPI_IN pin is made ‘0’. The address of the register

being read out is sent immediately after this control bit (MSB first). After the LSB of the address bits, the data is launched

on the SPI_OUT pin on the falling edge of the SPI_CLK. This means that the data should be sampled by the receiving

system on the rising edge of the SPI_CLK. The data comes over the SPI_OUT with MSB first. When reading out the

temperature sensor over the SPI, addresses 126 and 127 should be read-out in burst mode (keep SPI_EN high)

3.10 REQUESTING A FRAME

After starting up the sensor (see Chapter 3.7), a number of frames can be requested by sending a FRAME_REQ pulse.

The number of frames can be set by programming the appropriate register (addresses 70 and 71). The default number

of frames to be grabbed is 1.

In internal-exposure-time mode, the exposure time will start after this FRAME_REQ pulse. In the external-exposure-

time mode, the read-out will start after the FRAME_REQ pulse. Both modes are explained into detail in the chapters

below.

3.10.1 INTERNAL EXPOSURE CONTROL

In this mode, the exposure time is set by programming the appropriate registers (address 42-44) of the CMV2000.

After the high state of the FRAME_REQ pulse is detected, the exposure time will start after a delay of 133 clock cycles,

see AN16 – Exposure Timings for all the timing details. When the exposure time ends (as programmed in the registers),

the pixels are being sampled and prepared for read-out. This sequence is called the frame overhead time (FOT).

Immediately after the FOT, the frame is read-out automatically. If more than one frame is requested, the exposure of

the next frame starts already during the read-out of the previous one.

FRAME_REQ

Exposure time

Frame1_cycle

FOT

Read-out time

Exposure time

Frame2_cycle

FOT

Read-out time

FIGURE 13: REQUEST FOR 2 FRAMES IN INTERNAL- EXPOSURE-TIME MODE

FRAME_REQ

Exposure time

Frame1_cycle

FOT

Read-out time

Exposure time

Frame2_cycle

FOT

Read-out time

FIGURE 14: TWO REQUESTS FOR 1 FRAME IN INTERNAL EXPOSURE MODE

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