help - 11/34 console problem

Gooijen, Henk henk.gooijen at
Thu Nov 3 01:26:54 CST 2005

Tony wrote:
> 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.

  thanks Tony!

- Henk.

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