Qbus split I&D?

John Wilson wilson at dbit.com
Tue Mar 17 15:04:59 CDT 2015

On Tue, Mar 17, 2015 at 12:39:21PM -0700, Guy Sotomayor wrote:
>The parts that I've been looking at have unlimited write endurance and >20
>year data retention.

I'd be slightly worried that there are conditions being assumed here, even
if the MRAM data sheet doesn't seem to say so.  F-RAM claimed unlimited
writes, but under slightly cherry-picked conditions that might be exceeded
after all.  You could certainly write the whole memory from beginning to
end all day long, but whaling on just a small area (like the stack) could
be trouble.  Obviously I hope I'm wrong -- MRAM *looks* wonderful!

I used battery-backed SRAM in the Unibus RAM card I prototyped a while back
(and just recently got working and have been finishing the XMOS firmware
for).  The SRAM is cheap and fast and draws hardly any current (so it's
nothing like a lead-acid BBU setup -- AAs are fine and a CR2032 might even
last a while, so I've got one dangling off for testing to see if Rev B
should have coin cell holders), and once the battery is there, it's a nice
excuse for a TOY clock (my favorite KDJ11E feature that all PDP-11s would
benefit from).

John Wilson
D Bit

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