Kryoflux or Catweasle

Paul Koning paulkoning at
Wed May 24 14:51:22 CDT 2017

> On May 24, 2017, at 3:35 PM, Chuck Guzis via cctalk <cctalk at> wrote:
> I suspect that a PDP-11 in FPGA is quite a bit more reliable than the
> real thing--and when you're done you have a nice abstract description of
> the hardware in VHDL format.

The trick is to get it close enough to correct, given the documentation lapses.  The PDP-11 is better off than many other machines (VAX and Alpha are better still) because it has an architecture manual, but even that is not 100% complete. is a nice example of an FPGA PDP-11 (actually, the whole family -- conditional compile the model you want).  It seems pretty accurate; the fact that it runs RSTS is a good sign since that tends to be about as picky as any PDP-11 software you'll find.

> And yes, I have a pile of old CMOS/ECL/TTL logic.
> Remember when CMOS logic was new-- +15V Vdd and 1MHz top speed?

No, but I remember CD4000 series logic: Vdd anywhere between 3 and 18 volts -- crank up the voltage if you want it to go faster ("less slow").


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