Registration Integration
Time
The pixel’s integration time (the time needed for one frame reading) must be as regular
as possible to obtain consistent fingerprint slices. This time is directly dependant on the
SCK, SPI clock and frequency. Therefore, the SPI cycle of 4 × 8 × 233 clock pulses
should be as regular as possible.µ
Figure 17. Regular Integration Time
Regular Integration Time
Frame n
Frame n+1
Frame n+2
Frame n+3
Clock SCK
500 µs max
4 x 8 x 233 =
7456 Pulses
7456 Pulses
7456 pulses
7456 Pulses
233 = 232 + 1 Dummy Column
Note:
The 500 µs duration corresponds to the host’s computation time (slice reconstruction, finger detection…) and in the illustration is
given as an example only. Once the host detects a finger, this value remains constant, thus guaranteeing a regular integration
time.
Navigation (Slow SPI)
The sensor’s navigation function includes the processing elements necessary for pro-
viding the displacement of the finger touching the sensor in an up or down and right or
left direction. It is aimed at a screen menu navigation or simple pointing application. In
addition, a click processing function is embedded to detect a quick touch of the finger on
the sensor. It is aimed at screen text, box or object selection. A double-click function
could also be implemented in the software.
This interface has been designed to resemble the PS/2 mouse protocol.
An interrupt signal IRQ indicates to the host that an action has been detected. The host
must read the status register to obtain details on the action. The IRQ signal enables
implementation of an efficient power consumption protocol.
Note:
•
•
Click and navigation modes can be used together.
Two configurations are implemented for the click and navigation modes:
–
Stream mode, where the sensor sends an interrupt to the host when a
movement or a change in the button’s state is detected.
–
Remote mode, where the sensor does not interrupt the host but waits for its
registers to be read.
In these two modes, the registers are initialized after each reading from the host.
See “Appendix D” on page 38. for an example of an interrupt generated by a movement
detection.
30
AT77C105A [Preliminary]
5419A–BIOM–01/05
ATMEL [ ATMEL ]
