In SX Microcontrollers, SX/B Compiler and SX-Key Tool, robotnerd007 wrote:

I am working on a project that uses a US digital 400ppr to measure distance and then at two preset values it puts a pin to high in order signaling a basic stamp which takes care of everything else. I am not very experienced programming at all but feel comfortable enough with the basic stamp and have the code i need for that is working. However my code for counting the encoder pulses and signaling the basic stamp does not work. For counting encoder pulses i took the code from an encoder thread listed under "the best SX threads" I kind of understand how it works but could not write it myself.  I have channel A of the encoder connected to RA0 and channel B is connected to RA1. I was wondering if someone could take a quick look at this and point out my stupid mistake.  A big thank you to anyone who takes the time to help a beginner. 
P.S. Is there any reason not to run the sx at 50mhz? Would i have to change anything except the initializing code at the beginning? (i do know how to do that) 


' BLINK1.SXB
DEVICE          SX28, OSC4MHZ, TURBO, STACKX, OPTIONX
FREQ            4_000_000


EncPort         VAR     RA                      ' encoder port
TRIS_Enc        VAR     TRIS_A
MaxVal          CON     255
 EndVal         Con     400
SlowVal         Con     300
'encCheck VAR Byte
EncodersOld     VAR     byte                 
EncodersNew     VAR     byte                  
Encoder_A_Count VAR     word 
tmpB1           VAR     byte
tmpB2           VAR     Byte
tmpB3           VAR     Byte
 
' =========================================================================
INTERRUPT
' =========================================================================
' Runs every 64 uS @ 4 MHz (no prescaler)
ISR_Start:
 EncodersNew = EncPort
 TmpB1 = EncodersOld XOR EncodersNew ' compare old with new
                                     ' to work out which channels have changed
 TmpB2 = TmpB1 << 1   ' make single bit that shows change on A or B phase
 TmpB1 = TmpB1 OR TmpB2
 EncodersOld = EncodersOld << 1  ' make direction bits by comparing old A with new B
 EncodersOld = EncodersOld XOR EncodersNew ' xor old A with new B
 IF TmpB1.3 = 1 THEN
     IF EncodersOld.3 = 1 THEN
   INC Encoder_A_Count                         
     ELSE
   DEC Encoder_A_Count                          
      ENDIF
  ENDIF
 EncodersOld=EncodersNew
'ISR_Exit:
  RETURNINT                                   
' =========================================================================
  PROGRAM Start
' =========================================================================
 
Start:
                             
 
  EncodersNew = EncPort
  EncodersOld = EncodersNew
  Encoder_A_Count = 0

  OPTION = $88                                  ' interrupt, no prescaler 
bgn:
Do                        
If Encoder_A_Count >= EndVal then goto stop    'tells BS2 when to slow down and when to stop a robot
IF Encoder_A_Count >= SlowVal then goto slowdown
loop

stop:
 high RC.7 

slowdown:
high RC.6
goto bgn

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