TSL2569CS datasheet(34/56 Pages) OSRAM

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[v1-00] 2016-Apr-12

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TSL2568, TSL2569 − Application Information: Software

Interrupts

The interrupt feature of the TSL256x device simplifies and

improves system efficiency by eliminating the need to poll the

sensor for a light intensity value. Interrupt styles are

determined by the INTR field in the Interrupt Register. The

interrupt feature may be disabled by writing a field value of 00h

to the Interrupt Control Register so that polling can be

performed.

The versatility of the interrupt feature provides many options

for interrupt configuration and usage. The primary purpose of

the interrupt function is to provide a meaningful change in light

intensity. However, it also be used as an end-of-conversion

signal. The concept of a meaningful change can be defined by

the user both in terms of light intensity and time, or persistence,

of that change in intensity. The TSL256x device implements two

16-bit-wide interrupt threshold registers that allow the user to

define a threshold above and below the current light level. An

interrupt will then be generated when the value of a conversion

exceeds either of these limits. For simplicity of programming,

the threshold comparison is accomplished only with Channel

0. This simplifies calculation of thresholds that are based, for

example, on a percent of the current light level. It is adequate

to use only one channel when calculating light intensity

differences since, for a given light source, the channel 0 and

channel 1 values are linearly proportional to each other and

thus both values scale linearly with light intensity.

To further control when an interrupt occurs, the TSL256x device

provides an interrupt persistence feature. This feature allows

the user to specify a number of conversion cycles for which a

light intensity exceeding either interrupt threshold must persist

before actually generating an interrupt. This can be used to

prevent transient changes in light intensity from generating an

unwanted interrupt. With a value of 1, an interrupt occurs

immediately whenever either threshold is exceeded. With

values of N, where N can range from 2 to 15, N consecutive

conversions must result in values outside the interrupt window

for an interrupt to be generated. For example, if N is equal to

10 and the integration time is 402ms, then an interrupt will not

be generated unless the light level persists for more than 4

seconds outside the threshold.

Two different interrupt styles are available: Level and SMBus

Alert. The difference between these two interrupt styles is how

they are cleared. Both result in the interrupt line going active

low and remaining low until the interrupt is cleared. A level style

interrupt is cleared by setting the CLEAR bit (bit 6) in the

Command Register. The SMBus Alert style interrupt is cleared

by an Alert Response as described in the Interrupt Control

To configure the interrupt as an end-of-conversion signal, the

interrupt PERSIST field is set to 0. Either Level or SMBus Alert

style can be used.

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