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Richard King
09/11/06 13:01
Read: 2481 times
La Hulpe

Msg Score: +2
 +6 Informative
 -3 Overrated
 -1 Message Not Useful
#124088 - P0 not low enough (0.85V)
An unusual post, this, with problem & solution in one go!
I'm working on a hand-wired proto ("simple" serial-parallel converter to stretch a data bus). Initially, the processor wouldn't run at all, but finally it did (first warning, I guess). Then I could not get the P0 outputs low enough, even with just a pull-up (didn't forget those!). An activity led via a 74HCT04 on P0.6 flashed as required, serial out worked most of the time (warning 2?), but the 74HCT138s on the other P0 bits just wouldn't select anything.
After searching here (not wishing to post before checking!), I finally got that intuitive flash that we all get from time-to-time (it needs 0V to pull down to 0V), & noticed that there was no 0V connected to the 89C52!! Works a treat now! Tears of joy (& pangs of hunger, too!).

As usual, you just have to hang in there. It's only hardware & software, & it *always* works in the end!

Richard in Belgium

List of 24 messages in thread
P0 not low enough (0.85V)        Richard King      09/11/06 13:01      
   ?      Steve M. Taylor      09/11/06 19:07      
   Not useful? Overrated??      Andy Neil      09/11/06 19:17      
   Diodes      Oliver Sedlacek      09/12/06 04:05      
      A path to GND would still be needed      Kai Klaas      09/12/06 09:42      
         paths to GND might be fatal      Jan Waclawek      09/12/06 09:55      
            Thanks for the tip      Mahmood Elnasser      09/12/06 12:34      
            Rather low ohmic path      Kai Klaas      09/13/06 07:52      
   thanks      Jan Waclawek      09/12/06 05:04      
      if that is so      Erik Malund      09/12/06 05:55      
      P0 - all's well      Richard King      09/12/06 11:54      
   Another Thanks      Charles Bannister      09/12/06 05:10      
      Richard, I hope you are well now      Erik Malund      09/12/06 06:06      
   not necessarily for long      Erik Malund      09/12/06 12:04      
      Aware of that!      Richard King      09/12/06 12:42      
   Isn't this whole thing rather silly?      Richard Erlacher      09/13/06 09:32      
      good practice, Richard...      Jan Waclawek      09/13/06 09:38      
      Nooooooo...      Kai Klaas      09/13/06 11:10      
      Newbies aren't rigorous!      Jon Ledbetter      09/13/06 11:15      
         That\'s one place where we can help them!      Richard Erlacher      09/13/06 11:34      
      still glad I posted this one!      Richard King      09/13/06 11:49      
         it's maybe better      Jan Waclawek      09/13/06 14:04      
         It's a silly mistake, but one we've all made!      Richard Erlacher      09/13/06 16:49      
            the definition of experience:      Erik Malund      09/14/06 06:02      

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