| ??? 08/03/07 22:48 Modified: 08/03/07 22:51 Read: times |
#142744 - Here\'s what I want from you ... Responding to: ???'s previous message |
Jan Waclawek said:
Richard,
regardless of how does or does not a reset circuit work under insufficient power, one thing is absolutely sure: you cannot power up the mcu properly without a valid reset pulse as per datasheet. An another thing is absolutely sure: an RC reset does not provide a valid reset pulse as per datasheet, unless you have absolutely perfect control over VCC (i.e. a specified rise time and a guaranteed time gap between powerdown and powerup or no powerdown during the whole lifetime of device) - which may happen, but very rarely. Even in those cases, powerdown IS problematic, but that changes nothing on the fact: RC RESET IS NOT A RESET. We can continue to discuss the topic further publicly or privately, if you want; but don't expect big shifts in my position; nor groundbreaking proofs of anything - I don't have time to play with these things, sorry. JW Jan, Clearly you, and others, seem to continue to misunderstand what I want. I don't expect any sort of proof, since most people aren't interested in providing rigorous circuit characterizations. I'd like to know what direct observations you and others in this forum have made regarding this repetetive problem of RC vs. supervisor-generated RESET. I don't deny that there's been a problem, and I don't deny that some people have installed circuitry of various sorts in an effort to remediate the observed problem. I don't even deny that it has met with their satisfaction. A number of times, the "RESET" issue has become entangled with corruption of internal FLASH and/or other memory content. As you know, I believe the rise and fall times of Vcc have a great deal to do with this combination of symptoms. As I've probably mentioned several times, I've observed that 805x's sometimes corrupt battery-backed external RAM. I don't believe this to be an entirely RESET-related matter, as I've found this to be the case with both RC-reset applications as well as those using various supervisors. My sample, is small however, and, so far, my observations are pretty limited in number. As you say, no matter how we slice it, a reset pulse that meets the manufacturer's specifications is required. However, I think you've "muddied the waters" with the statement that the RC reset fails to deliver the specified RESET pulse, as the RC circuit is universally used as the recommended circuit. Not one manufacturer seems willing to "go out on a limb" and state that some other circuitry is required. That doesn't mean your assertion is false, but it does mean that it is confusing to those who don't understand the basis, and it is a conflicted one, on which you present that assertion. I do believe that you categorical statement, "RC RESET IS NOT A RESET" is patently incorrect, simply because it sometimes IS a reset. The RC circuit should, indeed produce the nominal, and within-specified-limits RESET pulse if Vcc has settled, for example, when you push the reset button. What I want, prior to setting up a length and involved long-term test of the RESET behavior of typical 805x-variants, is information about why people believe the problems they've seen are all RESET-based. I'm particularly interested in why they think it's RESET and not simply the Vcc rise and fall times, both of which can have an effect on reset and both of which can, in fact, impact the behavior of a supervisor IC. RE |
