DEC code was a nightmare. Any DG Nova line code would run on any machine. -John
============= > Hi > > The PDP-8 had so much code that depended on un-documented instructions > that they had to include them in later versions of the machine.... > > Bob > > > > On Aug 14, 2010, at 12:01 PM, "J. Forster" <j...@quik.com> wrote: > >> I think you missinterpret what I meant. Two examples: >> >> I've seen programmers who use "instructions" that are not part of a uP >> instruction set and are undocumented, just to be "clever". If a >> different >> brand of chip, or even a different rev., the chip does something >> completely different. These guys should be strung up by their tender >> parts. >> >> I've also seen transistors used as avalanche switches (basically a >> failure >> mode). If a different production run has improved normal mode >> performance, >> the avalanche function may vanish. >> >> FWIW, >> >> -John >> >> =============== >> >> >> >>> J. Forster wrote: >>>> FWIW, IMO any engineer who uses undocumented or uncontrolled >>>> parameters >>>> or >>>> instructions in a production design is a fool. >>>> >>>> If you are that silly, you must fully specify the selection criteria. >>>> >>>> -John >>>> >>> >>> Or, has their back against the wall and can't do it any other way. >>> >>> How is this any different than using trimpots or hand select? >>> >>> >>> For years, folks have hand selected matched pairs of devices, since the >>> circuit requires tighter tolerances than the mfr guarantees. >>> >>> Many, many RF designs have "select at test" pads to set levels or >>> tuning >>> stubs depending on what the actual gain or impedance properties of the >>> active devices are, or for trimming temperature dependencies. >>> >>> >>> Would you say that the engineer is a fool for not just specifying >>> tighter tolerances.. the tighter tolerances may not be available from >>> the mfr (who has to respond to many customers, most of which will be >>> happy with the standard performance). It's sort of a tradeoff.. do you >>> go to the mfr and say, I need a better grade of part, or do you buy the >>> run-of-the-mill part, and sort them. >>> >>> You might decide to do the latter for competitive reasons, e.g. rather >>> than the mfr producing a better grade of part, and potentially selling >>> it to your competitors too, you keep the "secret sauce" in house. >>> (Granted you could have the mfr make/select a proprietary part for >>> you.. >>> that's basically changing who does the work, but doesn't change the >>> underlying design) >>> >>> Even manufacturers do this, for instance with speed grades on things >>> like microprocessors. They don't have enough process control to >>> guarantee a particular speed, so they make em all, and then sort them. >>> >>> >>> The other thing is that the selection criteria might not be knowable in >>> a standalone sense. That is, you have to put the part into the circuit >>> and see if it works, rather than measuring some device parameter. I >>> would agree that to a certain extent, this implies that you don't >>> really >>> know how the circuit works, but it might also be that the most cost >>> effective approach is to use empiricism, rather than analysis. >>> >>> >> >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.