Page 173 - Build Your Own Quadcopter_ Power Up Your Designs with the Parallax Elev-8

152 Bu il d Y o ur O w n Q u a d c o p t e r

long cog
long fcPin ‘ frequency counter pin
long fcCycles ‘ frequency counter cycles

PUB init(p) : okay
‘’ Start frequency counter on pin p
‘’ -- valid input pins are 0..27

if p < 28 ‘ protect rx, tx, i2c
fcPin := p
fcCycles := 0
okay := cog := cognew(@frcntr, @fcPin) + 1
else
okay := false

PUB cleanup
‘’ Stop frequency counter cog if running

if cog
cogstop(cog~ - 1)

PUB period
‘’ Returns period of input waveform

return fcCycles

PUB freq | p, f
‘’ Converts input period to frequency
‘’ -- returns frequency in 0.1Hz units (1Hz = 10 units)
‘’ -- should not be called faster than expected minimum input
frequency

p := period
if p
f := clkfreq * 10 / p ‘ calculate frequency
fcCycles := 0 ‘ clear for loss of input
else
f := 0

return f

DAT

org 0

frcntr mov tmp1, par ‘ start of structure