servo on a PIC

Controlling a Servo using PicBasic Pro

The principles of controlling a servo from a PIC asre the same as from a BX-24, Basic stamp or any other microcontroller. See the motor control notes for more on this.You need to give the servo a 1-2 millisecond pulse once very 18-20 milliseconds.

Using PicBasic Pro, the command needed is the PulsOut command. With a 4-MHz clock, the pulsOut can generate a minimum 10-microsecond pulse, so the values below are given with that in mind. With a 20-MHz clock, the PulsOut command can pulse as short as 2 microseconds, so you will need to adjust the minimum and maximum pulsewidths (multiplying by 5 should do the job):

start:
	pulseWidth var byte
	' set up constants with the minimum and maximum pulsewidths
	minPulse CON 50
	maxPulse CON 250
	' set up a constant with the time between pulses:
	refreshPeriod CON 20
	
	' set an initial pulsewidth:
	pulseWidth = minPulse

main:
	'take the output pin low so we can pulse it high
	Low PORTC.3
	' pulse the pin
	PulsOut PORTC.3, pulseWidth
	' pause for as long as needed:
	Pause refreshPeriod
	
	' change the angle for the next time around:
	IF pulseWidth > maxPulse Then
		pulseWidth = minPulse
	Else	
		pulseWidth = pulseWidth + 1
	Endif
	
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