Hijacking (restarting?) an old thread from the Yahoo! list in 2016 (copied below). I was interested in contacting Jon about his
3850/3853 project. The 3850 is better known as the Fairchild F8 processor (1977), which appeared on the scene only slightly later than the 1802.
Unfortunately it seems that (based on net-research) Jon passed away earlier this year. kenneke.com has gone offline (final wayback:
https://web.archive.org/web/20200201071950/http://www.kenneke.com/), his mail server is no longer responding, and there is a more-or-less corresponding obituary posted (https://www.newsbreak.com/oregon/albany/news/1582571130390/jon-keith-fromherz-kenneke).
Could be a terrible coincidence, of course. If so then Jon please-speak-up! Otherwise, my condolences to his family and friends. Seems to have been a real nice guy, as well as an intermittent contributor here.
Was anyone here perhaps in communication with Jon about his project, including the 6502 to F8 assembly converter, or knows more about his effort?
If so could you share that information? Thank you,
From: cosmacelf@... [mailto:cosmacelf@...]
Sent: Thursday, December 22, 2016 10:05 PM
To: joshbensadon@... [cosmacelf]
Subject: Re: [cosmacelf] Re: Diode OR gates for address decoding?
Thanks for the input. I looked around on the 'net a bit. I didn't see
(find) any examples of an address decode using diodes. I'm sure it's
This is yet another of my 8-bit projects. This time it's a 3850/3853
MOSTEK chipset which is NMOS. Everything else (RAM/ROM/UART) is CMOS.
So, the diode drop should not be a problem.
I thought about using Schottky diodes.
I just figured out a way to do this with one 74LS32. Only one gate on the
chip is used as an actual NOR; the three others are used as inverters.
One of these days, I'll try the diode OR as an address decode in a working
circuit, like my little Z80 board. It's an interesting idea when you need
just one more OR.
Now to write the 6502 to F8 assembly converter. Ha!
On Thu, 22 Dec 2016, joshbensadon@... [cosmacelf] wrote:
> Hi Jon,
> That should work fine on some logic families, pick the right resistance for
> the pull down.
> First, with TTL, the Voh is about 3.6volts, so a diode with .7V drop will
> loose too much to drive the Vih input of another gate. In any case, you
> really want to minimize that diode drop, I believe the Schottky diodes drop
> only 0.2V, But even with that drop, it's not good news in TTL. But I'm
> certain you can get away with using it on CMOS circuits. Now the pull down
> resistor will have to be chosen to provide a fast enough discharge of the
> capacitance of the input circuit ie it needs to be low enough to drop the
> voltage fast, but high enough to not significantly load down the A14/A15
> I wonder if there are available circuits to copy from the internet?
Posted by: jon <jon@...>