Timers example. By Lee Davison
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Introduction.

In this example the SuprDupr is used to read a joystick on an analog input and generate a servo PWM signal using two of the timers.

The joystick input gave a value of 90 to 165, the servo needs a pulse width of 0.5mS to 2.5mS which, with the prescale value used, means TIMERX values will range from 50 to 250

The values for S and M, the scaling and minimum offset values used in the code, were calculated as follows..

S = timer range / input range
  = (250-50) / (165-90)
  = 2.67

.. and ..

M = minimum timer - minimum scaled value
  = 50 - (90*S)
  = -190

10 REM generates timing pulses for a servo 20 REM control is via analog input 0 30 REM output is via timer X 40 REM timer 1 is used to generate the 20mS frame 50 REM 100 TIMERX STOP : REM stop output 110 PRES12 49 : TIMER1 199 : REM set TIMER 1 for 20mS timebase 120 M = -190 : REM set minimum pulse width offset 130 PS = 4 : REM set timer X prescale value 140 S = 2.67 : REM set scale value 150 PRESX PS : REM set timer X prescaler 160 X = 0 : REM set input for timer X 180 TIMERX PULSE : REM timer X to output pulse 190 GOSUB 1010 : REM calculate initial X value 200 ON TIMERX 1000 : REM stop timer and calculate next 210 ON TIMER1 2000 : REM set and start TIMERX 220 DO : LOOP : REM just loop forever 997 REM 998 REM TIMER X routine 999 REM 1000 TIMERX STOP 1010 LX = A2D(X) : REM read port 1020 LX = LX*S : REM scale value 1030 LX = LX+M : REM add minimum width offset 1040 RETURN 1997 REM 1998 REM TIMER 1 routine 1999 REM 2000 TIMERX LX : REM set timer X 2010 TIMERX START : REM start timer 2020 RETURN

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