OK. *** PLEASE LISTEN *** The following is mainly written to Olin It's a genuine attempt to analyse what "went wrong" in this case and to see if we can achieve a degree of understanding that may lead to better results in future. This is long. I don't expect that many will want to read through it and follow my technical points but I really do hope that Olin will. This is not an attempt to win points, get smart or be seen as right etc. I think that what I am saying here is, in this case, technically correct. I do think that Olin misconstrued somebody's response and that it led to problems. I do hope that in this case Olin will actually admit he was wrong and apologise - and that he will do so happily (enough :-) ) in this case - because I see that despite his "pugnacity" he can actually front up to things when required. The hope is that this may actually lead to more productive future outcomes for all..We'll see. For reference - this is the material that got this going. [Robin] >> I am surprised by the blowing of the chip on 12V applied to MCLR [Olin] > You shouldn't be. This is very clearly spelled out in the datasheet righ= t > where you'd look for it. The third line down under Absolute Maximum Rati= ngs > specifies -300mV to 6V as the range. Since 12V > 6V, there should be no > surprise that it goes poof at 12V. > Or if I got this wrong I apologize, but then please do show us a copy of > your personal exemption certificate for being allowed to violate the laws= of > physics. Note that there IS an apology there already. But it is qualified by an impossible request (" ... but then ...") so let's lay that one aside for now. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D I wasn't meaning to be argumentative for the sake of being so. First the "PC" preamble: - then the technical analysis. It DID seem to me, and I'm sure it would to a significant percentage of others, that you were trying to be picky in a pointless way with the statement made. Listen again / still. That statement is also not meant to just be 'stroppy'. It really did seem that way. This is, perhaps, just part of the differences in human nature. I have to lean quite hard against my perceptions to see that question as you apparently do and to see you answer as anything like reasonable. BUT I can see that it can be done. My point is that we all MUST try to lean towards the other perspective more than is comfortable if we are to get on. And I believe that you (Olin) need to try to lean harder than most for several good reasons. This is not meant to be unfair, it's meant to be an attempt to reflect reality as I see it. Which won't be quite as you see it :-). The following especially applies when you don't quite understand what the other person actually means or has clearly enough said - as does happen on occasion :-). - There are fewer people who are comfortable from the extremes of your perspective than otherwise. - The rapidly occurring damage and negative effects on the people who can't comfortably play in the same arena than you is much greater than that which occurs to eg you when SOMEWHAT DIFFERENT approaches are taken. - You are more able to take the short term "damage" while a mutually agreed understanding is reached. This thread is an excellent example: In this case YOU are wrong technically, by your own measures (see below). I suggest that you read through the following, see if you agree with me and then, if you do, and if you are happy to do so, actually apologise for having taken a wrong perspective and having reacted as a consequence. You, unlike most, have a thick enough skin to do this (apparently :-) ) and it would possibly be a major step towards finding some middle ground in such things:. LISTEN: The above also isn't meant to be rude or trying to win cheap points. It's an attempt to show how a technical perspective that you have taken and a failure to think through the overall point being made has lead to you saying something which is very minor to you but which may be major to someone else. Or may not. You are unable to see how devastating quite apparently minor "rebukes" may seem to others. CONSIDER - look carefully at what was said: Words in [] are mine. Statement: I am surprised by the blowing of the chip on 12V applied to MCLR REASON: as [1] all inputs are [ARE] protected by static protection diodes [2] which can usually handle several mA [3] which is below the current limit of most programmers. Query: Do you know if the J series is different on this pin ? ___ You then "addressed" his surprise, said that he shouldn't be and queries his reading of a data sheet, desire to use a device well over its rating etc. Essentially, none of what you said he said was actually said. I'll quote the technical part of your reply in full: // .... how does that apply to 12V on MCLR when the absolute maximum rating is= 6V? That's way beyond the rating, not just less than a diode drop so nothing ba= d will probably happen, most of the time. I'm guessing that on the 3.3V only parts, MCLR does have a protection diode like the other pins. Raising it to 12V therefore effectively applies over 11V Vdd to at least part of the chip. That is so far outside spec it is very likely to cause damage. Whether the excess current blows the protection diode or the excess voltage blows up the rest of the chip I wouldn't guess on. Either way the chip is damaged. // If you work through what was originally said you'll see that you and the original questioner are in technical agreement OR are making statements which are technically NOT mutually exclusive. But he seems to have possibly (literally) read the data sheet better than you have. LISTEN: As above - not an attempt to win points etc - an attempt to see how we got here and whether we should have (uphill both ways/lake/cardboard box ...). YOU are not obliged to read the data sheet. It is entirely acceptable for you to make technical assumptions as long as they are clearly stated. It's best if the assumptions have a reasonable prospect of being correct. But all this applies to the questioner as well. AND he did state assumptions - he didn't use the term "assumption" or "query" - he stated his assumptions as a probability and he made a statement of fact based on (apparently) having read the data sheet - and the statement was in complete accord with what you said subsequently - BUT you used the very assumption to criticise him. viz: HE said that the pins all DO have protection diodes. YOU said "I'm guessing that on the 3.3V only parts, MCLR does have a protection diode like the other pins" You are both in agreement. His crucial assumption, that made his surprise at least reasonable (and in no ways in conflict with the laws of physics) was - " ...all inputs are protected by static protection diodes which can usually handle several mA which is below the current limit of most programmers." Pedantically you could say that he meant "above" where he wrote "below" but his point is entirely clear. He is saying that the protection diodes will USUALLY sink more current than MOST programmers will source AND IF SO, the pin will be clamped to a diode drop above Vdd AND SO the IC would not be expected to die BECAUSE the absolute rating of voltage and current has not been exceeded. His "surprise" does not mean he thinks you should do this, it does not say that it is technically impossible for the observed result to occur - he is saying that BASED ON THE DATA SHEET no worst case values would be exceeded in MANY cases and you could reasonably expect to "get away with" such a (moronic :-) ) act in many cases. To me it seems that his key assumption (which he stated) is that the programmer max current is < the protection diode max current. It appears that this is not the case in this instance and that damage occurred. His "surprise" therefore revolves around his belief in his statement re the 12V drive capability of "most programmers" If you had "addressed" him on the validity of that assumption we may have had a reasonable discussion. Maybe :-). But instead you assumed that he was saying something which he didn't say, you made the same assumptions as he did and were in technical agreement with him but you missed his point and then argued expressly against what he said usnig the very thing he agreed with you on (diodes being there). Even then - if your language had been that of B Franklin and not B Goldwater it may have been amicably resolved. But, as most people hear what is said re assumptions etc as challenging and rude and ... we are off again. Human nature at work :-). (Your statement re the laws of physics was in the same gist as the song "Are you going to Scarborough Fair?" - it takes what sounds like an apology and instead turns it instead into a claim that the questioner is stupid- if that comment had been left off then the statement would not have been overly confrontational [Parsley, Sage, Rosemary & Thyme ...] ). SO - IF you agree with me in what was actually said, [[ ie Protection diodes which are present on MCLR have a current rating which is in excess of the source capability of most programmers so the pin may well be clamped to a diode drop above Vdd without causing damage]] and that it was reasonable enough, and that the assumptions were clearly enough stated (you don't have to agree that they are correct, and that effectively you failed to work through what was said and thus "addressed him:" for the technically wrong reasons, you may decide that you are able to and should apologise in this case. It might be the start of a better understanding all round. The alternative seems for you to either ignore all this (tempting :-) ) or to explain in depth why you were correct and he was wrong etc. Your choice. Russell -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .