20

Frame Capture

This is a fast way to download a full array of pixel values

from a single frame. This mode disables navigation and

overwrites any downloaded firmware. A hardware reset

is required to restore navigation, and the firmware must

be reloaded afterwards if required.

To trigger the capture, write to the Frame_Capture

register. The next available complete 1 2/3 frames (1536

values) will be stored to memory. The data are is retrieved

by reading the Pixel_Burst register once using the normal

read method, after which the remaining bytes are clocked

out by driving SCLK at the normal rate. The byte time

before the data is ready, it will return all zeros.

To read a single frame, read a total of 900 bytes. The next

636 bytes will be approximately 2/3 of the next frame.

The first pixel of the first frame (1st read) has bit 6 set to

1 as a start-of-frame marker. The first pixel of the second

partial frame (901st read) will also have bit 6 set to 1. All

other bytes have bit 6 set to zero. The MSB of all bytes is

set to 1. If the Pixel_Burst register is read past the end

of the data (1537 reads and on) , the data returned will

be zeros.

After the download is complete, the micro-controller

burst mode. The read may be aborted at any time by

raising NCS.

Alternatively, the frame data can also be read one byte at

a time from the Frame_Capture register. See the register

description for more information.

Figure 24. Frame capture burst mode timing

NCS

address

data

address

address

MOSI

SCLK

P0

P1

P899

MISO

>120ns

frame capture reg write

enter burst

mode

Notes:

1. MSB = 1 for all bytes. Bit 6 = 0 for all bytes except pixel 0 of both frames which has bit 6 = 1 for use as a frame marker.

2. Reading beyond pixel 899 will return the first pixel of the second partial frame.

4. This figure illustrates reading a single complete frame of 900 pixels. An additional 636 pixels from the next frame are available.

pixel dump reg read

P0 bit 6 set to 1

all MSB = 1

see note 2

soonest to begin again

frame capture reg

exit burst mode

≥10μs

≥10μs

≥50μs

≥4μs

≥10μs

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PixArt Imaging Inc.

PixArt Imaging Inc.