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???
07/13/06 11:53
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 		 #120178 - RTFM
Responding to: ???'s previous message
Harshada D Nehete said:
the fault onyau is referring is correct when i mean processor fault i refer to the fault which occurs if the processor stops

What fault do you suspect that would cause this?

Note that the AT89S51 Watchdog is clocked from the system clock - so, if that stops, the watchdog will also stop!

and not faults that will occur due to software bugs or infinite looping.

AT89S51 Datasheet, p8, said:
The WDT is intended as a recovery method in situations where the CPU may be subjected to software upsets.
(my emphasis).

if i use the watchdog timer the processor gets reset as soon as there is an overflow.

Correct - that is what the datasheet says.

i want to illuminate an led and then wait for hardware reset to restart the processor.how is this done .

You would need external hardware to spot the reset, and hold the reset line low until required.

is there a location in the controller where the processor jumps if there is an watchdogtimer overflow

No: the watchdog asserts the reset line - as described in the Datasheet

where i can illuminate the led and wait for the reset pin to reset it

You've got into this state becuase the processor hardware has stopped - you said it's not a software lock-up.
So how can the processor do anything if it is stopped?!

You are going to need some sort of external "supervisor" to do this.



List of 30 messages in thread
TopicAuthorDate
processor fault            01/01/70 00:00      
   Use Watchdog            01/01/70 00:00      
      Not necessarily            01/01/70 00:00      
         Spec of AT89S51            01/01/70 00:00      
            Still too specific            01/01/70 00:00      
   There is no one such thing!            01/01/70 00:00      
   Undefined state !            01/01/70 00:00      
      processor fault            01/01/70 00:00      
         RTFM            01/01/70 00:00      
            reset            01/01/70 00:00      
               Read the data sheet            01/01/70 00:00      
                  WD with indication            01/01/70 00:00      
                     I, too, can visualize some exotic conditions where            01/01/70 00:00      
                        to bite or not to bite            01/01/70 00:00      
                           the REAL issue            01/01/70 00:00      
                              Marketing trick            01/01/70 00:00      
                                 to be dramatic            01/01/70 00:00      
                                    It is helpful, of course.            01/01/70 00:00      
                                 let's put it this way:            01/01/70 00:00      
                           I doubt that it's 10 transistors ...            01/01/70 00:00      
                              the context            01/01/70 00:00      
                     Can you name an example of this sort?            01/01/70 00:00      
                  reset            01/01/70 00:00      
                     AT89S51 WD            01/01/70 00:00      
         How do you propose to make the processor "illumina            01/01/70 00:00      
   Software hang-up, hardware lock-up            01/01/70 00:00      
      How about redundancy?            01/01/70 00:00      
         paranoia            01/01/70 00:00      
            ... but it WILL detect a processor fault!            01/01/70 00:00      
               The ultimate misconception            01/01/70 00:00      

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