5 Apr
1999
5 Apr
'99
2:23 a.m.
So I've got a Q-bus system with 64KW (128KB) of RAM
that is allegedly an 18
bit backplane. When I'm in ODT I can type:
@177770/
And enter values for 1777772, 1777774, 1777776, and then it wraps around to
000000.
If I start at 200000 it works until 3777777 and then wraps to 2000000. So
it seems to not cross a 64KB boundary.
That's how it's supposed to work. If you look in the tech manual for the
processors, you see that there's a 16-bit register for the "low" part
of the ODT address, and another register for the high part of the ODT address,
but there's no carry connecting the two.
Also the boot area is 177300 ? so it
is in the upper 4K of the 64KB address space, is it legal to have memory
"above" the I/O page?
Absolutely. In fact, some configurations had only a 2Kbyte I/O page
to allow a little bit of extra memory, and this still works (albeit not
officially supported) under RT-11 (it was tested before the 5.7
release.)
--
Tim Shoppa Email: shoppa(a)trailing-edge.com
Trailing Edge Technology WWW: http://www.trailing-edge.com/
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