FPGAs and PDP-11's

From: Allison J Parent <allisonp_at_world.std.com>
Date: Sun Aug 29 21:51:08 1999

<Allison wrote:
<> I'd start with a 32bit PDP-8 (just add 20 more bits on the right side).
<and in another posting:
<> Me I'd do a stretch-8 for fun. though yours sounds interesting too.
<A Stretch-8 would require too much time spent on hacking -8 software for m
<taste. Why not just build the equivalent of one of the DEC 18-bit family
<members (PDP-4, -7, -9, or -15), since the PDP-5 and -8 are basically a 12-
<version of the PDP-4. Then your project is at least compatible with
<something, and can run some existing software (operating system, macro
<assembler, Fortran).

Several reasons. Don't know the 18 bit machines at all. I would want a
machine that would fit in nx4 or nx8 format parts. I'd want a really
simple instruction set as that simplifies the hardware ruling out the
10, 11 and vax. So streatching an 8 is it.

Now a stretch-8 would have software as the bits added would only impact the
address field. Makeing the top 5 bits and the bottom 7 behave as the normal
8 would make code port fairly reasonable. I've always found the 8 limiting
in only one way, address space. Basically the Nova is a similar idea
stopping at 16 bits.

Received on Sun Aug 29 1999 - 21:51:08 BST

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