VD5377 Datasheet, PDF (37/88 Pages) STMicroelectronics – Ultra-low power motion sensor for optical finger navigation

VD5377
Key features
6.7
Automatic/manual frame rate
The VD5377 can operate in either automatic or manual frame rate control mode. The default
frame rate control mode is automatic (see Table 21, register 0x1c bit 4). This means that the
device adjusts frame rate automatically depending on the tracking velocity. By default, frame
rate is adjusted in the range 1 k to 2 k to Max. Because power consumption increases as
frame rate increases, automatic frame rate control is the most efficient in terms of power
consumption and requires no additional overhead from the host CPU. The maximum frame
rate to be applied in auto frame rate mode is set with register 0x1c bits 7:5. The default
maximum frame rate is 3.3 kf/s. Manual frame rate is selected with register 0x1c bits [2:0].
Table 21. Adaptive frame rate control
Addr
(Hex)
Register name
Signal name
Bit
Type
Default
(Hex)
Comment
frame_rate_sel
1c
FRAME_RATE_CONT
ROL
frame_rate_ctrl
2:0 PRW
4 RW
Frame rate selection (value for
internal osc running @48 MHz)
0 = 0.5kf/s (2 ms period)
1 = 1 kf/s (1 ms period)
2 = 2 kf/s (500 us period)
02 _{3 = 2.5kf/s (400 us period)}
4 = 2.9kf/s (350 us period)
5 = 3.3kf/s (300 us period)
6 = 3.6kf/s (275 us period)
7 = 4 kf/s (250 us period)
Frame rate management control
0 = Automatic (1 k / 2 k / Max f/s
00 auto frame rate)
1 = Manual (set with
frame_rate_sel reg)
max_auto_frame_r
ate
7:5 RW
Maximum frame rate to be applied
in auto frame rate mode.
0 = not allowed
1 = not allowed
2 = 2 kf/s (500 us period)
05 _{3 = 2.5 kf/s (400 us period)}
4 = 2.9 kf/s (350 us period)
5 = 3.3 kf/s (300 us period)
6 = 3.6 kf/s (275 us period)
7 = 4 kf/s (250 us period)
Due to CPU bandwidth limitations of the on-board MCU, maximum frame rate is limited to
3.3 kf/s in sunlight timing mode. In Normal DMIB timing mode only (default mode - register
0x51 = 0), the maximum frame rate may be increased up to 4 kf/s but in order to meet
internal timing constraints, the maximum exposure time (EXPOTIME_MAX 0x49) needs to
be reduced according to Table 22. The motion_threshold_low_comp (SPARE 0x32) should
also be updated.
Doc ID 022952 Rev 2
37/88