AT77C104B datasheet(25/36 Pages) ATMEL

25 / 36 page

AT77C104B

5347B–BIOM–08/04

Figure 14. Fast SPI Communication

Communication Speed

The acquisition speed of the pixels is linked to the clock’s communication speed. The

faster the communication clock, the faster the authorized maximum finger sweeping

speed. The sensor supports fast communications up to 16 Mbps.

Reading of Frame

A frame consists of 232 true columns and 1 dummy column of 8 pixels of 4 bits each. A

frame starts with a dummy column.

Figure 15. Example of a Frame

The first dummy column, at the beginning of the pixel array, is added to the sensor to act

as a specific easy-to-detect pattern, and represents the start of the frame tag.

The pixel array is always read in the following order: the first byte, following the 4 bytes

of the dummy column, which contains the value of the pixels physically located on the

upper left corner of the array, when looking at the die with bond pads to the right. Then

another 4 bytes are read that contain the value of the pixels located in the same column

from top to bottom. The next column on the right is output, and so on, until the last line

on the right, close to the bond pads, is output.

Even values are first sent during the data serialization for SPI transfer. Therefore, the

synchronization sequence on the chip’s MISO output is F0F00200.

Bit2

Bit3

MSB

Bit1

Bit0

Bit3

Bit2

Bit1

Bit0

Bit2

Bit1

Bit0

Bit3

Bit2

Bit1

Bit0

Bit3

MSB

SCK (Pixel Clock)

MISO

Transmission Clock

Edge (Sensor)

Reception Clock

Edge (Host)

Pixel 2i

Pixel 2i - 1

Pixel 2i + 2

Pixel 2i + 1

Pixel Frame

p10

p11

P12

P13

P14

P15

p16

Synchro = F0F00200

Dummy

Column

232 x 8 Pixels Column

AT77C104B Datasheet(PDF) 25 Page - ATMEL Corporation

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