help - 11/34 console problem
henk.gooijen at oce.com
Thu Nov 3 01:26:54 CST 2005
> Do you have a logic analyser? If so, then I would try looking
> at the 8080 address bus. See what bit of the program it's
> executing, see if it does the right things when you press the
> keys, etc.
Yes, I have a Biomation D250 I got from Edward recently.
However, I think I am not yet out of all options to pull out the
"big gun". First I must hjave a look at the printset to see how
the keyboard scanning works, but I suspect that the signals are
generated by the 8008. Makes sense to me ...
If I am lost, I will pull the D250 out (and the manual, because
I will need to study/learn how to use the beast).
> If you don't have a logic analyser, a trick that's helped
> many times before is to connect an n-bit comparator to the
> address bus, with the otuer input from switches. You can use
> that to see if the processor ever accesses a particular
> address (e.g. to see if a particular routine is being executed).
I used that method to detect why my homebrew 68010 did not work.
I was used to 680x devices, so I programmed the 68010 software to
set up the stackpointer at the highest RAM location. Big mistake!
It should have been highest minus 1 (even address aligmnent!),
but that's another story. Btw, the 68010 works fine :-)
> I am pretty sure it doesn't do UNIBUS accesses when you type
> in a number.
> Firstly, it doesn't know when you've finished the number
> (until you press onoe of the other keys), and secondly, the
> number you type in may well not be data for the current
> addresss -- it might be a new address, or a value to put into
> the Switch Register.
Yes, that is what I was thinking too.
> I wonder, though, if the thiog needs signals from the arbiter
> to work properly. I can't see why it would, but maybe if one
> of the bus lines is in the 'wrong' state it gets very confused.
Ha, this sounds interesting. Although I removed most of the cards
out of the backplane, there are still a few that could hurt if
the arbiter fails, because of wrong bus lines IF they play in
this scheme. Again, I must dive deeper into the M7859 diagram.
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