ggs at shiresoft.com
Tue Mar 8 12:47:46 CST 2016
> On Mar 8, 2016, at 10:39 AM, Jay West <jwest at classiccmp.org> wrote:
> Guy wrote...
> The 11/20 can address only 32KW (64KB). You need an MMU to access more.
> So MEM11 doesn't have a MMU "on board" then, got it.
The MMU is a CPU function.
> Just curious... I seem to recall you were having trouble fitting all the desired functionality on the UMF11, probably taking it out of the SPC form factor (or something similar).
> Would moving forward with your MEM11 as "the" memory option and then removing memory from the UMF deliverables - free up the silicon to solve the earlier size issue?
It doesn’t help. On the UMF11, I use a 256K x 16 FRAM for “memory”. Since the Unibus only can
only access 128K x 16, I’m using the other “half” of the memory for other stuff (J1 uCode images,
configuration settings, Boot ROM images, Console emulator ROM image, etc, etc). So it really doesn’t
save anything if I removed that functionality (the footprint of the 256K x 16 FRAM is the same as
the 128K x 16 FRAM).
There’s a lot of random crap that I have to deal with (5v to 3.3v translators) power supplies (3.3v,
2.5v, 1.8v), connectors for the SLUs, etc.
However, what I’m most worried about is power. According to DEC specs, an SPC board can only
draw 4 amps off the 5v supply. I’m not sure what the current draw will be. I’ll know more once I
build the prototype and can actually measure it.
TTFN - Guy
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