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

RTCC interrupt rates are independent of system clock frequency; that presumes that the given clock is fast enough to let the interrupts run completely before the next one is called. No way 100_000 will run at 4mhz with this kind of code. I would run at 20MHZ or better yet 50MHZ (which is what it looks like you're doing). If debugging, make sure the Key is clocking at 50mhz.

Second, and this prob. the cause of the problem -- you don't just want to wait for the ping response, you want to actually check that the ping line goes high THEN goes low, not just check for low. I am sure the ping will not respond in 10us after the trigger line goes low. The ping is programmed to *always* return some kind of high pulse, so you need to check for the edge before closing out the reading. Probably something like this:

[code]
 ' ----- End Pulse USD -----

    IF General_Var(1) = 3 THEN 			' waiting for high pulse on ping to finish triggering the USD       
   	IF Tix >= 1 THEN 			' 10us trigger
            LOW USD_Pin 			' end pulse
            IF Tix >= 2 THEN 			' wait for at least 10us low
               Tix = 0 				' clear the timer 
               rawdata = 0 			' clear the last measured value
               INPUT USD_Pin 			' make pin input
               General_Var(1) = 4    		' next state
            ENDIF
         ENDIF
    ENDIF


' ----- wait for pin to go high before waiting for sample -----
   
    IF General_Var(1) = 4 THEN 	
	IF USD_Pin = 0 THEN 		 'still low
		Tix = 0     ' keep the counts cleared
                rawdata = 0
        ELSE
		General_Var(1) = 5  'went high, wait and measure...
         ENDIF

     ENDIF

 ' ----- Measuring USD -----
   
    IF General_Var(1) = 5 THEN 			' measuring
	IF USD_Pin = 0 THEN 			' Signal is high as long as no feedback. Once USD receives something, then signal goes low. 
						' wait for pulse to end. only if pulse has ended, procedures goes ahead, otherwise abortion here
             led2 = ison
	     LOW USD_Pin 			' pulse ended: turn pin off to keep trigger low
             Distance = rawdata 		' move count to stable variable
             Tix = 0				' clear the timer 
						' from now on I have 5ms until the next reading of the USD (set at 1*)
     	     IF Tix >= 4000 THEN
		General_Var(1) = 2 				' end this step, skip the index finding step and system check
	     ENDIF
         
	ENDIF
   
     ENDIF

[/code]

---------- End of Message ----------


You can view the post on-line at:
http://forums.parallax.com/forums/default.aspx?f=7&p=1&m=394074#m401105

Need assistance? Send an email to the Forum Administrator at forumadmin@parallax.com

The Parallax Forums are powered by dotNetBB Forums, copyright 2002-2009 (http://www.dotNetBB.com)