EPROM emulator

[Ludis Langens]

Tom <thergen at svn.net> wrote:
> 
> A Cypress cy7c008 or cy7c009 might work
> 
> Accesses to the same address at the same time are a problem.  Since
> there's probably no way to make the ECM cpu wait, collisions would have to
> be avoided altogether or the ECM cpu should be able to terminate the other
> sides memory cycle if needed.

If there are two banks, one for the ECM, and one for downloading, then
there can't be a collision.

> The rams mentioned have access times of 20ns
> or lower compared to the 120ns needed, which may help in the logic design
> for the collision handling.

The P4's deselect the PROM for 120ns, but enable it for 360ns.  I don't
how much of the 360 is lost due to data setup time.  OTOH, the C3's
might not deselect the PROM at all between back to back accesses.  Which
brings up the point - it might be good to prevent a bank switch between
data read cycles of a "LDD $89AB".

john <jgwynne at mrcday> wrote:
> I had intended on using loadable
> shift registers to clock our data and reduce the routing.

I assume a shift register with tri-state outputs so that it can be
"half" of a mux?

> | Gee, this would be quite impressive, even when using SOP surface mount
> | parts!  
>
> Thank you... I once made a board with more than 40 chips too :) 
>
> Your point? If it takes 20 we'll use 20... if we can do it in less, we
> will.

Sorry, that was not intended as a sarcastic comment - it was meant as a
positive comment.  If there's a point, it is that this is hardly a KISS design.

David A. Cooley <n5xmt at bellsouth.net> wrote:
> Would have to be able to handle 512K Eprom (or nicer if it was programmable
> to what it would handle... up to 512 or 1024.)

I would expect that one version might handle 2732's, another 2764
through 27512, and a third for the 1024's.  The version might be
selected as the board is populated, or perhaps a switch or jumper setting.

Mike Pitts <mpitts at netspeak.com> wrote:
> My P4 uses a 64k byte EPROM (27C512).  Thats the reason I 
> can't use my Intronics emulator, it only goes to 32k byte.

This is a moot point, but is that really still a "P4", as opposed to a
P5, P6, or whatever?

Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/