Re: [N8VEM-S100:6630] Re: CPM3 memory banks

Subject: Re: [N8VEM-S100:6630] Re: CPM3 memory banks

Date: Sat, 21 Mar 2015 23:25:33 -0400

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Hi Bob --

>> I recall several months ago, in response to some of my more preliminary questions
>> on this group regarding bank switching, someone suggesting the use of the 74LS670.

That was me! I've been thinking about ways to do this (with the 74LS670 and a 512 x 8 SRAM) since then. Came up with this design, and put it together on a plugboard. I was surprised that it was so easy to get working! And at 10 MHz no less. The compact flash seems to work great too.

>> I have the feeling that a 48K Bank / 16K Common would be more appropriate for
>> CPM3. In that respect, I am designing my MMU to have a selectable common size:
>> 32K, 24K, 16K and 8K. It will provide bank-select for up to eight banks.

Will the 32/24/16/8k pages appear anywhere in the address space, or at a fixed location?

I think I might go back to Francis Gormarker's original design (16k pages), because that will permit bank swapping in the middle of the Z80's address space. Much more convenient. Or, maybe, try some tricks with the Z180??? Who knows.

Roger