****** Driving a servo directly **************
'********************************************** 
'@ Platform: PicBasic 
'@ Version: 1.0
'@ Author: Brian Patton (brianp@robodyssey.com)
'     Robodyssey Systems, LLC. - www.robodyssey.com
'@ Last Updated: Feb 19, 2004 
'*********Materials*****************************
' 1 Robodyssey PicPac MotherBoard
' 1 Pic16F876 or similar
' 1 Voltage Divider board
' 1 Variable Resistor (pot)
' 1 Servo connected to pin B4
' PicBasic Compiler and a programmer
'***********************************************
' Register Locations
Symbol  TRISA  = $85       ' Register Location of TRISA
Symbol  ADCON0 = $1F       ' Register location of ADCON0
Symbol  ADCON1 = $9F       ' Register Location of ADCON1
Symbol  ADRESH = $1E       ' Register Location of ADRESH
'***** Variables *******************************
Symbol MinPot = b4         'Value for the minimum of the pot
Symbol MaxPot = b5         'Value for the maximum of the pot
Symbol RPot = b6           'Range between Min and Max
Symbol ServoPos = b7       'Pulse the servos will use
symbol value = b8          'variable to hand off to
Symbol x = b1              'just a counter
'*****Initiation********************************
Init:
 Dirs = %11111111              ' Set all Port B to output
 
'*****Main Code Block Area**********************
'********* Calibrate Pots **********************
 Serout 0,N2400,("Calibate Pots",10,13) 'Display "Calibrate Pots" on the computer screen
 Pause 3000
Start:
  poke TRISA, %11111111      'Set all PortA Input
     poke ADCON1, %00000010 'xxxx0010 - PortA 0-4 analog inputs, 5-7 digital inputs 
                             '0xxxxxxx Sets result to Left justified
                             '1xxxxxxx Sets result to Right justified
Cal:
 b3 = 1                         'give it some start points
MaxMod:
 MaxPot = b3                    'give it some start points
MinMod:
 MinPot = b3                    'give it some start points
for x = 1 to 20                 'Give you time to turn the pot
     poke ADCON0, %11000001  'Set A/D to RC Osc, Channel 0, A/D converter ready
                                                'xx000xxx-Chan 0(RA0), xx001xxx-Chan 1(RA1),
                                                'xx010xxx-Chan 2(RA2), xx011xxx-Chan 3(RA3),
                                                'xx100xxx-Chan 4(RA4), xx101xxx-Chan 5(RA5),
                                                'xx110xxx-Chan 6(RA6), xx111xxx-Chan 7(RA7),
 
     b0 = %11000101                    'xxxxx1xx - on, xxxxx0xx - off
        Poke ADCON0,b0                 ' Turn on the conversion at Bit 2
 
calfin: 
  Pause 5
        Peek ADCON0,b0
   If b0 = %11000101 Then calfin       ' Wait for low on bit-2 of ADCON0, conversion finished
     Peek ADRESH,b3
  If b3 > MaxPot Then MaxMod           'Collect min and max values
   
  If b3 < MinPot then MinMod           'Collect min and max values
   
   Serout 0,N2400,("Min ",#MinPot," Max ",#MaxPot,10,13) 'Display min and max values on your screen
  pause 50
next
 Serout 0,N2400,("The Final Min ",#MinPot," Max ",#MaxPot,10,13) 'Display final min and max values on your screen 
 Pause 2000
 RPot = MaxPot - MinPot                             'Calculate the range
 Serout 0,N2400,("The Pot Range = ",#RPot,10,13)    'Display the Range
 Pause 2000
 RPot = 1200/RPot 'The 1200 comes from differece of the min pulse width and max pulse width recomended by the
                  'Servo manufacture time 10 in 10uSec units. The 10X is to keep the answer a 8 bit integer.
                  'So, a servo with a rated pulse of 0.0009 to 0.0021 is 90 to 210 ten uSec units.
                  'That is a difference of 120 uSec units. Times 10 is 1200.
      
 Serout 0,N2400,("The Multiplier = ",#RPot,10,13)   'Display the value from above
 Pause 2000
 Serout 0,N2400,("Calibration Finished",10,13)     'Display "Calibration Finished"
 Pause 2000
 
'******** Move the Servo **********************
AD0chk:
     poke ADCON0, %11000001  'Set A/D to RC Osc, Channel 0, A/D converter ready
                                               'xx000xxx-Chan 0(RA0), xx001xxx-Chan 1(RA1),
                                               'xx010xxx-Chan 2(RA2), xx011xxx-Chan 3(RA3),
                                               'xx100xxx-Chan 4(RA4), xx101xxx-Chan 5(RA5),
                                               'xx110xxx-Chan 6(RA6), xx111xxx-Chan 7(RA7),
 
     b0 = %11000101               'xxxxx1xx - on, xxxxx0xx - off
        Poke ADCON0,b0            ' Turn on the conversion at Bit 2
 
AD0fin: 
  Pause 5
        Peek ADCON0,b0
   If b0 = %11000101 Then AD0fin  ' Wait for low on bit-2 of ADCON0, conversion finished
     Peek ADRESH,b3
 
'************ convert value and ******************        
'************ drive the Servo ********************
 value = MaxPot + 10           'Hand over the value and keep it from ever becoming 0
 ServoPos = value - b3         'Subtract found value from the Max possible
 ServoPos = ServoPos / 10      'Correct the 10x thing from above
 ServoPos = ServoPos * RPot    'Multiply it by the range
 ServoPos = 210 - ServoPos     '210 is the longest pulse in 10uSec intervals my servo will handle
  Pulsout 4, ServoPos          'Pulse the Servo
'*************************************************
 goto AD0chk                   'Start it all over again
 end