Reproducing old machines with newer technology (Re: PDP-12 at the RICM)

Dave G4UGM dave.g4ugm at
Tue Jul 14 12:32:46 CDT 2015

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Chuck
> Guzis
> Sent: 14 July 2015 18:17
> To: General at; Discussion at and Off-
> Topic Posts
> Subject: Re: Reproducing old machines with newer technology (Re: PDP-12 at
> the RICM)
> I'm missing something in this discussion, I think.
> HDL's (take your pick) are just programming languages like FORTRAN or C
> with different constraints.  What's the point of going to all the trouble of
> doing an FPGA implementation of a slow old architecture, when pretty much
> the same result could be obtained by running a software emulator?  

I don't think this is true. Most of the software simulators don't run at anything like accurate speed ...

> Neither
> accurately reflects the details of the real thing--and there will always be the
> aspect of missing peripherals.

I believe that you can get much closer with an FPGA...

> Perhaps the worst aspect of using FPGA is that this is a rapidly moving field,
> so that the part you used to do your implementation 10 years ago
> will no longer be available.    

That is very true, but there again the same can happen with Software. The Pegasus Simulator I use was written in TurboPascal and has kludges to get the speed right that just don't work on a modern PC

> I've done a few designs using 5V CPLDs
> (XC95xx series) not *that* long ago.  Now they themselves are quaint
> examples of obsolete hardware.  You can't win.
> You can move software-only simulators quite easily, but I'm not as sanguine
> about FPGA designs.

See Above

> And you still don't have the peripherals.  I suppose one could emulate a
> Univac Solid State machine in FPGA, but what would one do about the all-
> important drum coupled to the card reader and printer.  Has anyone rolled
> out a design for a DIY 1403 printer?

When I have finished the Calcomp Plotter....

> I've run the Cyber emulator as well as various SIMH emulators from time to
> time, but it's just not the same as the real thing--it's not even remotely the
> same.

I have used Hercules with a real 3270. Its not bad but Laurence Wilkinson's 360 in FPGA wih a real Selectric Typewrite is much better:-

> --Chuck

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