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???
04/21/11 03:41
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#181959 - Timing
Responding to: ???'s previous message
A good reset circuit is needed to make sure the processor gets properly reset if VCC rises slowly or fast, or if there is glitches on VCC or if you turn off power for a very short time. The problem with RC solutions is that they can work perfectly for first-time power-on when the capacitor started out completely empty, but have huge problems with restarting the processor if you quickly disconnect/reconnect power. Note that contact bounce when turning on the power can result in failures with RC reset solutions because the first bounce may manage to charge the cap while the processor locks up during the short absence of power but don't get a second reset on the next bounce.

A real reset circuit should use active components, meaning that they can respond quickly in all conditions.

Anyway - I don't know what you mean with "commands" in your post. But if the processor boots but then runs differently far before hanging, then you probably have other problems. You might have marginal supply voltages. Or marginal timing on some critical signals (very important when using external memory). Or maybe the oscillator is running at wrong speed. Or maybe the oscillator isn't running stable.

Do you have proper decoupling on the supply voltages? Is your ground plane stable?

List of 22 messages in thread
TopicAuthorDate
Is 80C535 Compatible with 80C31?            01/01/70 00:00      
   do not use pin numbers            01/01/70 00:00      
      Supervisor Chip            01/01/70 00:00      
         you say you want to test chips            01/01/70 00:00      
            Reset Circuitry for 80C535            01/01/70 00:00      
               Timing            01/01/70 00:00      
               probably because ...            01/01/70 00:00      
                  Supervisor/Watchdog Timer chip            01/01/70 00:00      
                     No timer needed to kick watchdog            01/01/70 00:00      
                        The internal Watchdog Timer            01/01/70 00:00      
                           good choice            01/01/70 00:00      
                              NE555            01/01/70 00:00      
                                 8051 and 555 reset            01/01/70 00:00      
                                    555 Reset circuitry            01/01/70 00:00      
                                 bad choice            01/01/70 00:00      
                                    Reset Supervisor            01/01/70 00:00      
                                       there are other possibilities            01/01/70 00:00      
                                          Other source            01/01/70 00:00      
                     did the datasheet not say so?            01/01/70 00:00      
                        It says so            01/01/70 00:00      
                           would it not be a good idea to do so before ...            01/01/70 00:00      
         explain a bit about the nessecity of Supervisor Chip            01/01/70 00:00      

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