Re: OT: 68K core emulation (was Re: LisaEm 1.0.0-RC2 Available for download)

From: gilles <gilles.fetis_at_email.domain.hidden>
Date: Thu, 12 Jul 2007 13:57:44 -0700

On 12 juil, 16:02, Ray Arachelian <r..._at_email.domain.hidden> wrote:
> gilles wrote:
> > slowing down the cpu doesn't work for a 68k, due the the NMOS
> > conception. It should work with 68HC000 but I'm not sure the microcode
> > is exactly the same. So only a fast analyzer is a valid option.
> That's not true.
> The Lisa uses an 8MHz 68000, but clocks it at 5MHz due to memory bus
> sharing limitations, so it's certainly possible to slow down the CPU.

500KHz or 1 MHz may be possible, but under such values, some internal latches will lose information.
I think I have the datasheet somewhere.

> Slowing it down further is probably possible as long as the DRAM refresh
> is not disturbed, and the I/O is allowed to continue, but this is
> difficult to get right and still be able to run an OS that you can trace
> through and not worth the effort just to connect an umbilical cord to
> another machine. :-)

The screen will be the problem in this case... I don't think the lisa CRT will like to be slowed down too much...

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