strange number corruption on pdp11/34

Jacob Ritorto jacob.ritorto at
Wed Jan 28 21:29:52 CST 2015

>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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