Topics

3850/3853 Project (was: Diode OR gates for address decoding?)


Paul Birkel
 

All:

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,
paul

-----

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?

Josh,

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
there, somewhere.

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!

Jon

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
> lines. 
>
> I wonder if there are available circuits to copy from the internet?
>
> Cheers,
> Josh__._,_.___


Posted by: jon <jon@...>


joshbensadon
 

Hi Paul,

If it is the same Jon, then RIP Jon.

Looking through old emails, I can't find anything more.  But I did see a message where Jon said:
"Have not recieved the pushbutton, but mail is never expedient in this backwater town of Oregon."

Josh.



From: cosmacelf@groups.io <cosmacelf@groups.io> on behalf of Paul Birkel <pbirkel@...>
Sent: Monday, September 21, 2020 4:12 AM
To: cosmacelf@groups.io <cosmacelf@groups.io>
Subject: [cosmacelf] 3850/3853 Project (was: Diode OR gates for address decoding?)
 

All:

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,
paul

-----
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?

Josh,

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
there, somewhere.

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!

Jon

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
> lines. 
>
> I wonder if there are available circuits to copy from the internet?
>
> Cheers,
> Josh__._,_.___


Posted by: jon <jon@...>


 

  If you guys do anything interesting with the 3850, please let me know.  I've got a couple of MK38P70 parts here that need to have a job.  The MK38P70 is a 3870 MCU (an upgraded single chip 3850) with a piggyback EPROM socket on top of the chip.  The piggyback socket thing was a pretty unique idea at the time, but it never caught on.  The downside to the 3870 parts is that they have no ability to access external memory, so whatever you do has to fit within the onchip RAM and piggyback EPROM.

  I did some looking around years ago, and the only interesting things I could come up with to do with one was either a clock (easy, but not all that interesting) or a chess game.  Lots of chess games from the late 70s and early 80s were based on F8/3850/3870 MCUs, and the code for some of them is floating around the Internet.

Bob

 


Dennis Boone
 

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.

Free associating a bit, there's a hack to read code out of existing 3870
chips that I stumbled across years ago when looking for a way to read
the 3870s in my Syntor X radios. (Still haven't done that project,
sigh.)

http://www.seanriddle.com/f8.html

De


Tony
 

To continue the free association, when I was working on my Netronics Video Terminal, I discovered that it uses a 3870 pre-programmed as a Display Terminal Controller (part #DTC 14004).

Tony


Doug Jackson
 

I remember that the TRS-80 Model 1 used diode OR gates in its design.  I duplicated them for a Rockwell 65F12 system that I built as my final year engineering project.

Kindest regards,

Doug Jackson

ph: 0414 986878

Check out my awesome clocks at www.dougswordclocks.com
Follow my amateur radio adventures at vk1zdj.net

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On Tue, Sep 22, 2020 at 2:15 PM Tony <tony.hefner@...> wrote:

To continue the free association, when I was working on my Netronics Video Terminal, I discovered that it uses a 3870 pre-programmed as a Display Terminal Controller (part #DTC 14004).

Tony