AT77C104B_08 Datasheet, PDF (31/46 Pages) ATMEL Corporation – FingerChip Thermal Fingerprint Sweep Sensor, Hardware Based, Navigation and Click Function, SPI Interface

AT77C104B
14. Navigation (Slow SPI)
The sensor’s navigation function includes the processing elements necessary for providing 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 44. for an example of an interrupt generated by a movement
detection.
14.1 Navigation
See “Navigation Register” on page 21.
The typical navigation slice frequency has been fixed to 2.9 kHz. A programmable divider is
implemented in the control registers (NAVFREQ) to reduce this frequency. Finger displacement
is provided as a number of pixels in X and Y directions. Negative movements are possible. The
register is cleared after the navigation registers are read. These registers are incremented or
decremented between two accesses.
Table 14-1.
Navctrl
Register
(Bits b6 to b5)
00
01
10
11
Typical Navigation
Slice Frequency
(kHz)
5.8
2.9
1.9
1.5
Typical
Integration Time
(µs)
172
345
526
666
Typical Maximum
Finger Speed
(cm/s)
30
15
9.5
7.5
31
5347F–BIOM–3/08