Re: Proms bigger than 64K

[Peter Gargano <peter@techedge.com.au>]

Richard Wakeling wrote:
> 
> What happens when the chip is bigger than 64K?

Motorola have an application note about addressing 128k bytes of
RAM with an 68HC11 (as I understand the later GM CPUs are) - it's 
AN432/D. I pulled it off their web site a while ago, so check there.

> I noticed that the chip is sorta split into two parts, as if its two
> programs.

There will be some common code that flips between these two parts of 
the program. That code will be "mapped" to the same physical address
for each part. Somewhere in that common code will be a routine that
toggles the high order address line (say A15 for a 27512, or A16 for
a 27001), and this is what makes the swap between the pages.

HTH, Peter.
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