help - 11/34 console problem

Gooijen, Henk henk.gooijen at oce.com
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.

This message and attachment(s) are intended solely for the use of the addressee and may contain information that is privileged, confidential or otherwise exempt from disclosure under applicable law.  
If you are not the intended recipient or agent thereof responsible for delivering this message to the intended recipient, you are hereby notified that any dissemination, distribution, or copying of this communication is strictly prohibited.  
If you have received this communication in error, please notify the sender immediately by telephone and with a "reply" message.  
Thank you for your cooperation.






More information about the cctech mailing list