11/45 progress

Tony Duell ard at p850ug1.demon.co.uk
Wed Mar 2 17:32:34 CST 2005

> Based on the docs I got from Ashley I was able to re-arrange the memory 
> section to be sane, cards were in the wrong slots. I was also able to get 
> the jumpers set right on the G110 card. Now when I power up I can definitely 
> read core correctly. There's a random assortment of data in sequential 
> locations and returning to those same locations I always get the same value. 
> That's a plus.
> However, I can't store anything. Anytime I store a new value in a location, 
> that location gets all zeros. Moving to another location I get data, and 
> moving back - zeros. So it appears to be challenged in writing, but not 
> reading, memory. The plot thickens :)

Ah, but your memory is core, right? In which case, a 'read' is actually a 
write followed by a restore. Since you can read the same location and 
keep on getting the same data from it (you can do that, right?), the 
memory is basically working (for both read and write).

Now, Unibus lines are almost all active-low. The data lines certainly 
are. Which means that a word of 0's corresponds to all the lines being 
high. And they're pulled up by the terminator ,and pulled down by the 
drivers on one of the CPU boards. Maybe you've got an enable problem to 
that driver, or maybe the data input buffers on the memory are playing 
up, or....

You could try writing to something else (perhaps the data register on 
your conosle termial card) to see if you can write to anything on the 
Unibus. Or if you have a logic probe, you could see if the data lines 
pulse low when you try writing 1's to a memory location.


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