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Richard Erlacher
12/03/12 17:43
  12/03/12 17:44

Read: 928 times
Denver, Co

#188955 - Those aren't the "usual" 805x-core MCU's
Responding to: Kai Klaas's previous message
Two aren't 805x-core and the NXP unit is quite different in that is uses a low-going reset signal. If Intel had used a low-going reset signal, I'm persuaded these problems would not be an issue. For some reason, Intel liked positive-going reset and interrupts, which made them more costly and cumbersome to apply. For that reason, I, personally, have used Intel parts very seldom.

I used there 8287 to correct a layout error rather than respinning a board. I did use 8748-family parts a few times, and I used COTS (Multibus) Intel-MCU boards from time to time (seldom, as they were costly) for industrial applications. I did like, very much, to use their i80186 CPU, though.

Using Vdd-based reset always seemed silly to me, as Vcc wanders around quite a bit, even under normal circumstances. Vss, OTOH, remains quite well-defined throughout power-up and power-down.

Average designers often use a somewhat too-weak PSU, and compensate for the weak PSU by adding lots of Vdd-Vss capacitance. This makes the rise and, espacially, the fall-time of Vdd slow, as things stop draining the Vdd supply. I've had cases in which an all-CMOS circuit was in the mail for two weeks and ultimately returned, and even though it had only a 4.7 uF cap on Vdd, the clock/calendar was still very much in sync with the rest of the world, despite the fact no battery had been installed yet. More common, however, is the decay of Vdd taking multiple tens of seconds before it is below the level at which components can run. It's for that reason that I focus on the decay of Vdd when considering the flash-corruption issue.

I'm not sure why things continue after RESET is asserted. I'm not sure that this happens on all, or even many different MCU's, but I have seen it on several, albeit in the same physical circuit, and it was not FLASH but, rather, BBRAM that was routinely corrupted.

Clearly, this needs further examination.

I really do wish there were more 805x-core-specific information regarding rise and fall of Vdd. That's where I believe the gremlin lives.


List of 33 messages in thread
C8051F231 experiences      Daniel Contarino      11/30/12 14:43      
   another solution      Erik Malund      11/30/12 15:11      
   The probabilities are low...      Daniel Contarino      11/30/12 18:34      
      think about what happens when you add a finger      Richard Erlacher      11/30/12 22:55      
         The point is ...      Daniel Contarino      12/01/12 03:08      
            Yes ... the underlying issue is the flash ...       Richard Erlacher      12/01/12 11:28      
               Out of my office, but...      Daniel Contarino      12/01/12 14:05      
                  Don't think in Vcc, ESD or hum...      Daniel Contarino      12/02/12 09:24      
   Apparently several C8051F2xx parts have the same pinout      Richard Erlacher      12/01/12 14:25      
   Characteristic for in system programmable flash micros...      Kai Klaas      12/01/12 18:25      
      All too true ... sadly ...       Richard Erlacher      12/01/12 20:13      
         Power-on slope rate...      Kai Klaas      12/02/12 05:31      
            Sorry, my post should be here, no up there...      Daniel Contarino      12/02/12 09:58      
            Have you any basis for that rate?      Richard Erlacher      12/02/12 10:15      
               Vdd ramp time      Maarten Brock      12/03/12 06:15      
               Some datasheets show numbers...      Kai Klaas      12/03/12 07:05      
                  Those aren't the "usual" 805x-core MCU's      Richard Erlacher      12/03/12 17:43      
                     There aren't many "usual" 8051-cores anymore...      Kai Klaas      12/03/12 18:13      
                        How dangerous power ups can be...      Kai Klaas      12/04/12 06:20      
                           I believe it      Richard Erlacher      12/04/12 08:59      
                              (dV/dt) examples      Jim Granville      12/04/12 13:14      
                                 They don't know it either...      Kai Klaas      12/04/12 18:49      
                                    dV/dT etc       Jim Granville      12/04/12 21:39      
                                       reset request...      Kai Klaas      12/05/12 06:21      
                                          That's what disturbs me greatly      Richard Erlacher      12/06/12 00:19      
                                             It IS disturbing!      Kai Klaas      12/06/12 08:02      
                                                Where this began ... at least for me ...       Richard Erlacher      12/06/12 09:43      
                                                   So, you took the hard road...      Kai Klaas      12/06/12 10:41      
                                                      We've all had that experience       Richard Erlacher      12/06/12 16:23      
   probable cause      Brent Wilson      02/04/13 20:32      
      Brent, this is very nice      Erik Malund      02/05/13 06:38      
         forum no longer down      Maarten Brock      02/05/13 07:33      
      Thank you!      Daniel Contarino      02/05/13 15:04      

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