Well, I'm going to build a 16C77 version of the project,
to see if that chip's A-D works over the whole range.

Harold M Hallikainen wrote:

>         I have several products running the A/D on the 16c74 over the
> full 0 to 5V range.  I wonder about your lookup table.  any possibility
> you're going over a page boundary causing it to blow up?  What happens if
> you simulate dropping in higher values where you sample the A/D result
> register?

I'll have to learn how to inject values in the simulator.  Thanks.

>
>         As you suspect, IT OTTA WORK!
>
> Harold
>
> Harold Hallikainen
> harold@hallikainen.com
> Hallikainen & Friends, Inc.
> See the FCC Rules at http://hallikainen.com/FccRules and comments filed
> in LPFM proceeding at http://hallikainen.com/lpfm
>
> On Tue, 23 Nov 1999 14:53:13 -0500 "Thomas C. Sefranek" <tcs@CMCORP.COM>
> writes:
> >Well here's the story so far...
> >
> >NO JOY!
> >
> >I've employed all suggestions so far, silly or otherwise.
> >
> >Rebuilt another board to ONLY have the PIC, a bicolor LED, and a
> >clock.
> >STRONG Grounds PINS 19 and 8.
> >1 ufd caps on the A-D inputs. Low impedance, low noise power supply to
> >the A-D.
> >2 ea .1 ufd caps between PINS 20 and 19 (VDD& VSS) pins.
> >1 Mhz clock, machine cycles are 250 khz.
> >External V.Ref tied to VDD and bypassed with 1 ufd.
> >(Tried internal Vref to VDD also.)
> >
> >Symptoms:
> >System code works FINE up to 4.14 volts at the A-D input, when VDD is
> >5.000 Volts.
> >(All values output from the lookup table in that voltage range are
> >correct!)
> >
> >Increasing VDD to 5.25 volts get it work with A-D levels up to 4.38
> >volts.
> >(Seems to follow VRef. so it's not magically related to a sweet spot
> >voltage.)
> >But I still can't get the A-D to work on values (? within a diode
> >drop)
> >of VDD! ~.86Volts.
> >The software freezes!  (Latch up?)
> >(Lower the voltage on the A-D slightly, and the system resumes
> >processing...)
> >
> >I know it's dangerous to accuse but...  I'm SO FRUSTRATED!
> >I doubt  that ANYONE has this PIC working the FULL range of A-D!
> >(Including Microchip! as they suggested I buy the B version to fix the
> >problem!)
> >
> >PLEASE PROVE me WRONG by supplying a working system
> >for me to test my chip, or some other method of proving the chips
> >actually can work.
> >
> >I'm not a hacker, I've been doing assembly on Motorola processors
> >since
> >there has been
> >Motorola processors!  (6800)  I'm not bad in Electronics either, 30
> >years in R&D
> >RF, Radar, Laser, Video, Audio, Power supplies, Micros, computer
> >peripherals,
> >you name it, I've successfully designed and built it!
> > (And I CAN get a MC68HC11 to do full range A-D without breaking a
> >sweat!)
> >
> >Fess up!
> >--
> >Thomas C. Sefranek  WA1RHP
> >ARRL Instructor, Technical Specialist, VE Contact.
> >http://www.harvardrepeater.org
> >http://hamradio.cmcorp.com/inventory/Inventory.html
>
> ___________________________________________________________________
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--
Thomas C. Sefranek  WA1RHP
ARRL Instructor, Technical Specialist, VE Contact.
http://www.harvardrepeater.org
http://hamradio.cmcorp.com/inventory/Inventory.html