using new technology on old machines. Was: PDP-12 Restoration at the RICM

Dave G4UGM dave.g4ugm at
Mon Jun 15 08:35:19 CDT 2015

I don't think it is over kill. If you want over kill try this:-

and FPGA implementation of the Baby or SSEM which had 32x32 bits of RAM. The implementation uses around 1% of the Spartan 3E 1200K gates, and that includes the logic to generate the VGA which is around 50% of the circuit. I expect to get it on a 100K gate chip but that’s still over-kill.

I am also aware how HARD baud rate generator chips are. Firstly you need to know the multiplier, and then you need a crystal that can easily be divided. I looked on E-Bay UK and the cheapest dedicated baud rate generator was 10x the price of a Arduino Nano. Then I would need a crystal and the other bits to make the generator. I would expect the chip count on a dedicated baud rate generator board to exceed that of the Nano. Of course it is not original, but an authentic board would only use SSI TTL and where would one find that easily.

I personally think it is an appropriate cludge that allows de-bugging to continue and gives you time to work out what the best long term solution would be.


> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Johnny
> Billquist
> Sent: 15 June 2015 10:52
> To: cctalk at
> Subject: Re: using new technology on old machines. Was: PDP-12 Restoration
> at the RICM
> While I agree that as long as things can be restored it's not a real problem, I'm
> surprised that not more people consider it a serious overkill.
> We're talking about putting in a rather complex computer to generate a baud
> rate. Are people really that handicapped when it comes to building hardware
> nowadays? Are people aware how easy baud generators are?
> We're essentially talking about a clock, which can be found as a component
> (various oscillators), and then dividing it. There used to be chips around
> which did that part, and I would expect it to not be that hard to find some if
> you looked today. Many UARTs even comes with a clock divider built in.
> And that is it. When I build various Z80 systems, I usually had a Z80 CTC
> included, which I used for generating the baud rates.
> 	Johnny
> On 2015-06-15 02:52, Joe Lenox wrote:
> > I also think it is in the spirit of the computer - using what is
> > available to fix a problem at hand. I think the arduino was overkill
> > when an attiny (smaller, easier to hide) would probably serve just as well.
> >
> > If you have the ttl logic bits lying around and know how to use them, fine.
> > Still would probably need debugging.
> > On Jun 14, 2015 2:41 PM, "Simon Claessen" <simski at> wrote:
> >
> >> as long as it is done in a way that it can be restored to its
> >> original, i have no problems in using newer technology in older
> >> machines. we have a alix sbc build into our tek 4002a for
> >> demonstrational purpouses, all done without damaging or altering the
> original machine.
> >>
> >> On 14-06-15 17:25, tony duell wrote:
> >>
> >>>
> >>>   The ripple on the power supplies is still going lower as we put
> >>> more run
> >>>> time on the system. The power supplies are now within spec.
> >>>>
> >>>
> >>> Capacitors reforming naturally?
> >>>
> >>>   Warren made an Arduino based programmable baud rate generator
> that
> >>> works
> >>>> for both serial ports. After some debugging, it works nicely.
> >>>>
> >>>
> >>> I am sorry, but I find that obscene!. To use more components than
> >>> the rest of the machine
> >>> (probably) just for the baud rate clock is ridiculous. IMHO if you
> >>> are going to modify a vintage machine, particularly one as rare as a
> >>> PDP12, you should use the components that were available at the
> >>> time. It's not as if a programmable buad rate generator is hard to
> >>> make from TTL either. In fact given the Arduino thing needed 'some
> >>> debugging' it might well have taken less time to do it in hardware.
> >>>
> >>> -tony
> >>>
> >>>
> >> --
> >> Met vriendelijke Groet,
> >>
> >> Simon Claessen
> >>
> >>
> --
> Johnny Billquist                  || "I'm on a bus
>                                    ||  on a psychedelic trip
> email: bqt at             ||  Reading murder books
> pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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