AT77C105A [Preliminary]
Figure 13. Example of an 8-bit Access
Controller
FSS/ = 0
Sensor
Sending of Dummy Data
0b0000000
Reception of 2 Pixels
Sending of 2 Pixels (8 Bits)
End of
No
Communication
?
Yes
FSS/ = 1
During an 8-bit access, the sensor transmits two pixels (each pixel is coded on 4 bits).
Figure 14. Fast SPI Communication
SCK (Pixel Clock)
MISO
Bit3
MSB
Bit3
MSB
Bit2
Bit0 Bit3 Bit2 Bit1
Pixel 2i - 1
Bit0
Bit2
Bit1 Bit0
Bit1
Bit3 Bit2 Bit1 Bit0
Pixel 2i + 1
Pixel 2i
Pixel 2i + 2
Transmission Clock
Edge (Sensor)
Reception Clock
Edge (Host)
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
Dummy
Column
232 x 8 Pixels Column
p1
p2
p3
p4
p5
p6
p7
p8
P9
0
F
0
F
2
0
0
p10
p11
P12
P13
P14
Synchro = F0F00200
Pixel Frame
P15
p16
0
27
5419A–BIOM–01/05
ATMEL [ ATMEL ]
