27220 Parallax Inc, 27220 Datasheet - Page 117

• Manufacturer Part Number: 27220
• Description: BOOK STAMPWORKS
• Manufacturer: Parallax Inc

Specifications of 27220

• Accessory Type: Booklet
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• For Use With/related Products: StampWorks
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Not applicable / Not applicable

' -----[ Initialization ]--------------------------------------------------
Reset:
' -----[ Program Code ]----------------------------------------------------
Main:
Behind the Scenes
In the last experiment, we learned that the frequency of a signal is defined as the
number of cycles per second. We created a simple frequency meter by counting the
number of pulses (cycles) in one second. This method works well, especially for low-
frequency signals. There will be times, however, when project requirements will
dictate a quicker response time for frequency measurement.
The frequency of a signal can be calculated from its period, or the time for one
complete cycle as shown in the illustration below:
By measuring the period of an incoming signal, its frequency can be calculated with
the equation (where the period is expressed in seconds):
DEBUG CLS,
DO
LOOP
PULSIN FreqIn, 0, pLow
PULSIN FreqIn, 1, pHigh
period = (pLow + pHigh) */ Scale
freq = 62500 / period * 16
DEBUG CRSRXY, 15, 0, DEC period, CLREOL,
Frequency = 1 / Period
"Period.(uS)... ", CR,
"Freq (Hz)..... "
CRSRXY, 15, 1, DEC freq, CLREOL
' setup report output
' get high side of input
' get low side of input
' scale to uSecs
' calculate frequency
' display values