Re: Kit-Based Lisa

From: Kevin Keith <krfkeith_at_email.domain.hidden>
Date: Tue, 18 Mar 2008 12:33:53 -0700 (PDT)

The only parts that won't be like the real Lisa is the floppy drive and the video. Other than that, it will be exactly the same. Unless someone here knows where I can find a GCR floppy drive, I think this makes the most sense. Also, does anyone know if the technical documents for that COP421 is?

Thanks for the support!

On Mar 18, 1:54 pm, Ray Arachelian <r..._at_email.domain.hidden> wrote:
> Kevin Keith wrote:
> > Don't worry, I'm up to it!
> > My ideas on the floppy:
> > 800k flopies (yet alone 400k's) are pretty hard to come by.  Not
> > impossible, but kind of a hassle to get.  My idea is to use standard
> > PC floppy drives along with some sort of microcontroller.  For those
> > familiar with the MiniMig project, this would be similar to the floppy
> > module.  Essentially, the drive connects to a board containng some
> > sort of microcontroller (maybe a 6502 for notalgia's sake!)  and a
> > ROM.  The controller loads, unzips, or whatever the images then loads
> > them to the ROM.  The controller then emulates a floppy drive.  Thid
> > would speed up the lisa significantly, and two images could be put on
> > a 1.44mb floppy.
> Yeah, if you're willing to give up GCR compatibility, any simulated
> floppy will work.  The key is to be able to transfer real Lisa floppies,
> either in Disk Copy 4.2 image form, or some translated form to the system.
> It doesn't have to run from a 6504 CPU, it doesn't even have to emulate
> a 6504.  You could even use a single I/O processor to handle both the
> floppy and the COPS functions - it just has to be visible to the 68000
> code as both sets of devices, in the same way as the real 6504 and
> COP421 were.
> > The video:
> > what type of video output does the Lisa have?  Is it TTL (I know that
> > the Mac SE used TTL)?  I think it would be next to impossible to find
> > a TTL LCD (assuming that is the video output) that supports the Lisa's
> > funky rectangular pixels.  I think Ray's idea is the best one.
> You can interpolate/anti alias the pixels on the actual display end.  On
> the interface to the 68000 memory, you need something that copies a 32K
> chunk of memory pointed to by the the video display address register to
> whatever will do the real display.  This copy should happen 60x/second
> to keep timing consistent, and needs to refresh the status register
> properly.
> So I guess the real question then becomes at point does this thing stop
> being a physical Lisa and becomes an emulated one?
> How close to a real Lisa do you want to get to?  I mean, if you just
> don't care, you could always get a mini motherboard, slap on a flash
> based linux and copy LisaEm to it, but that wouldn't be a Lisa in kit
> form, it would just be a machine that happens to run Lisa software
> because it runs LisaEm. :-)
> So find the place where you're comfortable amongst the spectrum of
> actual 1983 Lisa and emulated Lisa running on an intel machine and build
> to that.
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