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Chapter 6: Radio-Controlled Systems and Telemetr y 149

if(phsa < 0) ‘ phsa is a phase lock loop register.
It is used to store a count
proportional to the high pulse width
leftLength := 0
phsa := 0

ifnot(ina[leftPinNumber] or not(phsa))
leftLength := ((||(phsa~)) / (clkfreq / 1_000_000))
leftTimeout := cnt

if((cnt - leftTimeout) > ((clkfreq / 100) * timeoutPeriod))
leftLength := 0

if(phsb < 0)
rightLength := 0
phsb := 0

ifnot(ina[rightPinNumber] or not(phsb))

rightLength := ((||(phsb~)) / (clkfreq / 1_000_000))
rightTimeout := cnt

if((cnt - rightTimeout) > ((clkfreq / 100) * timeoutPeriod))
rightLength := 0
I would like to point out that no assembly language code was required for this Spin
program, since all the timing was accomplished by using the built-in cog counters and

Figure 6.21 A Propeller Serial Terminal display of two servo channels.