sorry for top post-- coming from Android thing.
you definitely do not want RAM at $8000 because it will collide with the I/O block that is
decoded there. If you have mp-b back plane as you stated then i/o occupies $8000 to $9fff
and so RAM needs to start at $a000.
The modified mp-m is to make it decode at $a000 or above because the stock circuit decoded
on 4k boundaries from $0000 to $7000 only.
Chris
On August 7, 2016 1:56:14 AM CDT, Brad H <vintagecomputer at bettercomputing.net>
wrote:
So I have the 6800 almost fully working, however I've hit one snag. ?
I loaded some of the memory diags as a first test, from txt files
posted online. ?The first couple worked ok, but the third kept hitting
an error immediately on start. ?
I thought little of it and was eager to try a bigger program. ?I tried
Blackjack. ?However I noticed when it was loading.. instead of just the
cursor remaining beside my L until loaded, it began dumping random
stuff out.
So that's when I went back to that RAM test. ?I noticed it has having
the same issue with a certain range. ?I realized then that my single
RAM board was only covering from (I think) A000 up to but not including
C000.?
So I used the jumpers on my DRC 16k boards to fill in the blanks, so to
speak. ?But I'm stuck on the last one. ?The memory check now crashes at
address 8000. ?Because my last MPM board was modified, I'm not sure how
to get that particular range. ?I'm also wondering why I only get from
A000 to C000 on my other MP-M board. ?The 16k boards can be set for
wide ranges.. say 8000 through I think FFFF (can't look at the docs as
SWTPC.COM went down tonight). ?I'm assuming the smaller RAM boards
cover less? ?With three of the four installed, I can load a program via
txt file without error but cannot run it.. if I hit G it just freezes
there. ?So I'm not sure if I need to configure a ram board for $8000 up
to $A000 or if I potentially have another problem. ?And because the
MP-M boards are both modified.. I don't know what they are/were set up
to do.
Brad
Sent from my Samsung device