[Coco] How much memory

[Frank Pittel]

On Sun, Nov 28, 2010 at 08:51:53PM -0500, Aaron Wolfe wrote:
> On Sun, Nov 28, 2010 at 9:04 PM, Frank Pittel <fwp at deepthought.com> wrote:
> > On Sun, Nov 28, 2010 at 05:51:45PM -0500, RJRTTY at aol.com wrote:
> >> In a message dated 11/28/2010 5:35:23 P.M. Eastern Standard Time,
> >> cmayeux at msbministries.org writes:
> >>
> >> >Perhaps we could keep it at 2 megs to eliminate some  hardware
> >> >And software "backpedaling"... just a thought.
> >>
> >>
> >> I agree.   2 megs is plenty of memory for an 8 bit 2 mhz
> >> processor to run around in.....
> >> and it has a certain symmetry to it since the task registers
> >> will also be 8 bits in a 2 meg system...
> >
> > The coco3fpga can run the "6809" as a 25mhz cpu and doesn't have the limitation
> > of only being able to directly address 64K or memory!
> 
> The 6809 can only directly access 64k of memory whether it's in
> silicon, FPGA, or being emulated accurately.  This is a fundamental
> aspect of the chip, it is true of all 6809s everywhere in every
> application.
> 
> The CoCo allows you to use more than 64k by mapping in little pieces
> of a larger address space into the single 64k space the 6809 can
> actually talk to.  Giving it massive amounts of RAM doesn't change the
> fact that at no time will the 6809 ever seen more than 64k of it.
> This is not a function of an operating system or programming, it is
> simply how a 6809 works (and also how many other "8 bit" chips which
> had 16 bit addressing work).

That's only the case if the fpga "6809" is limited to a 16 bit address bus. :-)

The Other Frank