On Tue, Apr 28, 2009 at 5:49 AM, Anders Carlsson
<anders.carlsson@sfks.se> wrote:
> Yes, that is actually an idea I've been about to ask regarding your 1541IDE
> project now when IEEE drives came into the question; how much the DOS logic
> differs between a 8050 and a 1541.

The largest difference between the 1541 and any dual drive (including
the 8050) is that the 1541 has one CPU, and the dual drives (as well
as the D90x0 DOS board) have two CPUs - one for the IEEE side, one for
the drive side, with shared memory.  ISTR it's done with inverted
phase on the clock to prevent simultaneous access (and to avoid using
expensive dual-port memory).

> Anyway, I'm sure there are lots of things
> one can do if you only had the time and motivation.

Always true.

> By the way, this guy once built a portable PET. Well, more like "movable"
> because it consists of a 8032, a 8050 drive, possibly even a printer all
> built inside a huge box of Masonite, and wheels added to the box. Really
> huge piece, meant to be used in the field during artillery practises. I
> don't know what kind of data they would calculate or record during shooting
> practise, perhaps people would take breaks and play some games on the PET.

Wow.  That's large.  I've wanted a laptop-sized PET for a while, but I
think it would have to be a 100% new design that replicates the
functionality of a PET (unlike the C-64 laptop I saw pictures of
recently).  I suppose one could take a Universal PET board and make
the laptop base the same size (as large as some early laptops were),
and just have the screen lift off the base (instead of a clamshell
design), but except for the video circuit and maybe the analog bits of
the tape circuit, most of the PET is pretty obvious given the memory
map and the requirements of the VLSI chips.  With modern RAM and ROM
(i.e., one chip of each) and perhaps a GAL for address logic, 80% of a
PET could probably be made to fit in a board no larger than your hand
- even with a 6545, the video is still not trivial.

-ethan

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