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.