Subject:
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HB bootstrap problem when U6 installed
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Thu, 4 Feb 1999 03:01:32 GMT
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Original-From:
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Fred G. Martin <FREDM@MEDIA.MITihatespam.EDU>
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Viewed:
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1028 times
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i am guessing that some of the inputs to u6 are defective, causing it
to assert its outputs when it shouldn't. this could turn on the '244
input latch, driving the bus when it should not.
please check that pins 1 through 6 signals are oscillating (with the
chip removed and installed). with the chip installed, check that pins
7 and 9 are not pulsing--- should be high.
fred
> One of my students is having a problem in assembling their HB:
>
> Downloading and executing IC works fine _until_ U6 is installed.
> After installing U6 ('138) the GRN LED doesn't quite go off when
> putting the board in bootstrap mode, it glows faintly. And we can't
> download the bootstrap.
>
> If U6 is removed, everything is fine, the GRN LED goes off when put in
> bootstrap mode, all downloading is fine.
>
> We did have to change 6811s to get this far (original one didn't
> work), but it seems solid now, but only if U6 not installed.
>
> Any suggestions?
>
> --greg
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