strange number corruption on pdp11/34

Johnny Billquist bqt at
Thu Jan 29 07:48:57 CST 2015

Short question: What did you boot from? The same RL controller and disk 
you then wanted to run diagnostics on? Or did you have a second storage, 
from which you booted?


On 2015-01-29 04:29, Jacob Ritorto wrote:
>  From what I observed, this zeroed-out prompt was just another manifestation
> of the zeroes bug.  The values were there in memory and were supposed to be
> offered to the user but got blanked out with zeroes instead.  I had
> suspected this and just hit enter at the prompt and XXDP did, in fact,
> exercise the disk.  There were blinking lights and head noise, obvious work
> being done that wouldn't have, had there actually been real zeroes in the
> address and csr fields.  I might swap the bad cpu board back in and try
> again, but now that the problem has been isolated and removed, I'm inclined
> to just enjoy the pdp11 :)
> On Wed, Jan 28, 2015 at 10:19 PM, Rick Murphy <rick at> wrote:
>> At 07:34 PM 1/27/2015, Jacob Ritorto wrote:
>>> Johnny, I just took the defaults,
>>> BUS ADDRESS (O)  0 ?
>> What Johnny said. The prompt says "(O)", not "(0)" - the letter O for
>> Octal. The zero after that isn't a default, it simply means that the value
>> hasn't been set.
>> There is no default. Or at least no sane one. Zero in this case means that
>> it's writing to memory address zero for CSR. The diagnostic should reject
>> that, but diagnostics are notoriously user unfriendly.
>>          -Rick

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