Now *this* is cool

From: Chuck McManis <cmcmanis_at_mcmanis.com>
Date: Tue Aug 7 17:14:43 2001

At 07:32 PM 8/7/01 +0100, Tony wrote:
>FWIW, FPGA-based re-implementations of classic computers don't satisfy my
>interests either. For 2 main rasons :
>
>1) I don't have any machine (read : lusedoze box) that will run the
>development tools, so I can't get in there and 'tinker'

You assume too much Tony. The tools run on UNIX systems as well as Windows
machines. If you read the page on the PDP-8/X you will note that the author
wrote _his own_ tools and those of course you could run under RSX-11M.
Further it would be possible to port them to Fortran but that might be too
painful.

>2) You can't clip a logic analyser onto the internal signals of an
>FPGA... Remember I think of computers in terms of gates and flip-flops...

Actually this isn't quite true either. Especially with respect to the
Xilinx RAM based FPGAs. Those nets on your schematic can be "bound out" to
any spare I/O pin. Generally I/O isn't a killer if you're using a BGA package.

>I am not at all convinced that there will be a time when it will be
>impossible to keep something like a PDP11 running, either. All the chips
>in something like an 11/10 or 11/45 are documented. You could, if you had
>to, re-implement a single chip in an FPGA. Sure it would be a waste of
>FPGA, but if the time came when you couldn't get (say) a 74S181, and you
>needed one, that would be a way of keeping the machine operational.

There is the concern however that the only FPGAs you could get would run at
3.3V or worse 1.8V. The smallest one would probably be a 36pin SOIC package
that you would have to dig out your old microscope to solder on to an
adapter board of some type. I've suggested for a while that the Xilinx
folks should take their 9500 CPLD series, put it into 14, 16, 18, and 22
pin packages, surround the die with 74S TTL compatible i/os and then have a
machine that allowed you to type in the TTL part you wanted and push the
button. And "poof" you'd get one of those. They don't think there would be
enough of a market to justify the tooling costs.

--Chuck
Received on Tue Aug 07 2001 - 17:14:43 BST