Subject:
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Re: Downloader and a/d
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Fri, 18 Dec 1998 13:51:00 GMT
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Original-From:
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fthompson9@aolIHATESPAM.com
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Viewed:
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1294 times
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Cesar,
> > Another doubt is with the 68HC11 a/d range: I simply couldn't find it. Is it
> > possible to use 0/60 mV, 0/100mV or even 0/1V without external amplifiers?
According to my book, you can set the reference voltages to anything from
Vss to Vss + 6.0 V (notice that this is higher than Vdd). The A/D result is a
ratioatic comparison for the sample voltage to the references. Page 48 of the
technical manual shows that Vrh (analog Voltage Reference High pin 52) is
connected to +5 and that Vrl (analog Voltage Reference Low pin 51) is
connected to ground. To change the voltage reference range:
First get a good pin placement map and be sure you know which side is up.
It is wasy to get top view and bottom view confused and wind up tearing up the
wrong pins.
Second scratch the trace(s) leading to pin 52 (Vrh). (If there are two
traces, they will need to be reconnected with wire so that you are only
isolating the pin.)
Third solder a wire to pin 52 and connect it to your 100 mV reference.
(Use your favorite noise reduction technique {coax, twisted pair,...}.)
That should be all you need. My book does not mention a minimum voltage
(except that the references should stay between Vss and Vss+6). It says that
the A/D conversion is done with a "charge redistribution" system which should
be independent of the actual voltages used. But the truth to that depends on
the quality of the capacitors and voltage comparator used. Good luck!
Hope this helps
Pherd
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