TMG39921 datasheet(36/96 Pages) OSRAM

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ams Datasheet

Page 35

[v1-06] 2018-Feb-27

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TMG3992 − Detailed Description

An interrupt is generated based on the number of gesture

“datasets” results placed in the FIFO. A dataset is defined as

4-byte directional data corresponding to N-S-W-E (GDIMS = 0).

The FIFO can buffer up to 32 datasets before it overflows. If the

FIFO overflows (host did not read quickly enough) then the

most recent data will be lost. If the FIFO level, GFLVL, becomes

greater or equal to the threshold value set by GFIFOTH, the

GVALID bit is set indicating valid data is available, gesture in-

terrupt bit, GINT, is asserted, and if GIEN bit is set a hardware

interrupt on the INT pin will also assert. Before exit of gesture

engine, indicated by GVALID transitioning from high to low, one

final interrupt will always occur. This interrupt signals that data

still remains in the FIFO. Gesture Interrupts and Flags: GINT,

GVALID, and GFLVL are cleared by emptying FIFO (i.e. all data

has been read).

The correlation of motion to FIFO data (i.e. speed and direction

characteristics) is not obvious at first glance. As depicted in

Figure 37, the four directional photodiode sensors are placed

in an orthogonal pattern beneath an optical transparent

aperture.Diodes are designated as: N’, S’, W’, and E’. The 8-bit

results corresponding to each diode are available for sequential

read at the following FIFO register address locations: 0xFC,

0xFD, 0xFE, and 0xFF. After address 0xFF is read, additional

reads automatically increase the FIFO pointer and effectively

reset the register address to back to 0xFC. This allows for

continuous transfer of FIFO data without re-issuing chip and

memory addresses.

Ideally, gesture detection works by capturing and comparing

the amplitude and phase difference between directional sensor

results. The directional sensors are arranged such that the diode

opposite to the directional motion receives a larger portion of

the reflected IR signal upon entry, then a smaller portion upon

exit. In the example illustration, a North-to-South motion is the

result when a target enters the device field-of-view from N’

(North-Prime), progresses past W’ and E’, then exits over S’

(South-Prime).

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