June
2005, Issue 179
Precision
Frequency Meter
Cypress
PSoC High Integration Challenge 2004 Contest Winner
FREQUENCY
MEASUREMENT
In
Analog mode, the AC-coupled and AGND-biased frequency
input is fed to the high comparator (as used for time
synchronization processing in Time mode). The comparator’s
reference changes to 0.5 VCC (AGND) so that it generates
a digital version of the input signal. The comparator
output is fed out of a pin and fed externally to a digital
input.
In
Digital mode, the AC-coupled and AGND-biased frequency
input goes directly to another digital input. The digital
input signal is fed to the clock of the InputDivider
counter (8 bits). This counter also has an ISR to extend
it in software to a 24-bit counter. The InputDivider
terminal count controls the capture enables of the ClockCounter,
which allows the exact time of the start and end of
the input signal sampled cycles to be recorded. This
hardware setup enables the software to know how many
input signal cycles were sampled and the exact number
of reference clock cycles that these input signal cycles
took.
