Book Analog Interfacing to Embedded Microprocessors
ture to a square-wave output. The period of the output signal is proportional
to temperature. The MAX6576 has two pins that are tied high or low to select
an output range of 10, 40, 160, or 640 ms per °K.
Using frequency in this way permits a microprocessor to measure temper-
ature with a single pin. The microprocessor software can perform this mea-
surement in several ways.
In a microprocessor with capture capability, such as the microchip
PIC16C6x series, the sensor output can be connected to the microprocessor
input that is used for pulse capture. A simplified block diagram of such a
capture system is shown in Figure 4.1. Here, a free-running, 16-bit counter is
captured by a 16-bit register when the input frequency changes from the low
to high state. At the same time, a short pulse is generated to reset the counter.
In the example shown in Figure 4.1, one period of the input is 90 ms and
the second is 100 ms
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