TSL2583 Datasheet, PDF (19/33 Pages) ams AG – LIGHT-TO-DIGITAL CONVERTER

TSL2581, TSL2583
LIGHT-TO-DIGITAL CONVERTER
TAOS134A − JULY 2012
APPLICATION INFORMATION: SOFTWARE
Interrupts
The interrupt feature of the TSL258x device simplifies and improves system efficiency by eliminating the need
to poll the sensor for a light intensity value. Interrupt mode is determined by the INTR field in the INTERRUPT
CONTROL Register. The interrupt feature may be disabled by writing a field value of 00h to the Interrupt Control
Register (02h) 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 signal a meaningful change in light intensity. However, it can also be used
lid ^{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 TSL258x device implements two
16-bit-wide interrupt threshold registers that allow the user to define thresholds above and below a desired light
a 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
v _{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 because, for a given light source, the channel 0
ill ^{and channel 1 values are linearly proportional to each other and thus both values scale linearly with light}
intensity.
t To further control when an interrupt occurs, the TSL258x 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
G _{s 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
A ^t 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
s ^{n example, if N is equal to 10 and the integration time is 402 ms, then an interrupt will not be generated unless}
the light level persists for more than 4 seconds outside the threshold.
m ^{te The interrupt line goes active low and remains low until the interrupt is cleared by selecting the Special Function}
in the COMMAND register and writing a 0 to the Interrupt Clear field value.
a ^{n To configure the interrupt as an end-of-conversion signal so that every ADC integration cycle generates an}
interrupt, the interrupt PERSIST field in the Interrupt Control Register (02h) is set to 0000b. An interrupt will be
Technical ^{co generated upon completion of each conversion. The interrupt threshold registers are ignored.}
Copyright E 2012, TAOS Inc.
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