Analog Interfacing to Embedded Microprocessor Systems, 2nd Edition

Measuring Period versus Frequency

I worked on one system in which an analog value was converted to frequency.

The sensor circuit converted a mechanical change to a slight frequency shift in an

RF signal. The frequency value for several sensors was captured using a PLD and

then read by a microprocessor. A block diagram of the capture system is shown in

Figure 4.3. A counter was incremented by the frequency input. Once every

sample period, the count was captured in a register and read by the micropro-

cessor. In this case, the counter was never reset, but was allowed to roll over from

FFFF to 0000; the microprocessor took care of calculating the correct ...