Re: External KERNAL using a 6510

From: Nicolas Welte (
Date: 2000-09-01 13:08:29

Frank Kontros wrote:
> Spiro Trikaliotis wrote:
> > Well, I have to look if I will find that magazine at home and have a look at it.
> > I remember seeing such a schematic these days, but I don't remember if it was
> > RUN or 64'er...
> 64'er. Who would like to get the scanned image?

Frank, 64'er also had an external kernal module which was able to create
some sort of an external HIRAM signal, but their approach was very
different from the one in RUN. It is a very interesting circuit, that uses
DMA accesses to determine the state of the internal HIRAM signal. I suspect
that this is also the big drawback of that circuit: as I understand it, it
can only sample HIRAM once per scanline or even once per badline, and
therefore the stored HIRAM state will be wrong if it is changed internally
until the external circuit makes a new sample.

The RUN circuit uses an external 6510 that runs in parallel to the internal
one, but is not allowed to make write accesses or drive the data bus. the
only write accesses it makes are targetet at it's own internal processor
port register and thus it duplicates the internal HIRAM line perfectly. I
still wonder what they were trying to say about using that circuit on the
C128: is it not necessary to use the 6510 there, or is it not _possible_?
(I think it would malfunction anyway if 2MHz mode is enabled).

This message was sent through the cbm-hackers mailing list.
To unsubscribe: echo unsubscribe | mail

Archive generated by hypermail 2.1.1.