strange number corruption on pdp11/34

Jacob Ritorto jacob.ritorto at
Tue Jan 27 18:34:32 CST 2015

Johnny, I just took the defaults, thinking that maybe the real value there
(that was printing as zeroes) was intact.  In fact, the disk did run tests,
blinking the ready light ferociously.  Then reported all zeroes back :\

In a stroke of sheer weirdness, it also managed to boot 2.9BSD from an
rl02! It actually ran kind of normally.  Even got to multiuser mode and ran
and compiled a hello world test program I typed in myself using vi!  Crazy,

Per your recommendations, I'm going to try the small test programs with
math here, shortly; thank you.

Also, I grabbed a set of pdp11/34a boards from a dead (ps issues) machine.
Can I plug them straight into this blackplane that's currently housing my
misbehaving 11/34?  Backplane markings are very faded but seem to say


On Tue, Jan 27, 2015 at 6:13 PM, Johnny Billquist <bqt at> wrote:

> On 2015-01-28 00:05, Noel Chiappa wrote:
>>      > From: Johnny Billquist
>>      > If it comes as far as booting RSX as well as XXDP, there can't be
>>      > anything seriously wrong with the CPU...
>> Yeah, I see your point, but why all the zeros, then? That's what I could't
>> work out.
>> Anyway, it should be really easy to make sure e.g. ASH, MUL and DIV are
>> working; it's vaguely plausible that one of them is broken. (Unix V6, I
>> think,
>> might even boot even if MUL was broken. I know the bootstrap uses DIV, to
>> calculate the cylinder in the disk driver.) If not, cross that off the
>> list,
>> and try the next thing... Which is?
> Is noone paying attention to the fact (and my previous comment) about
> using 0 for CSR and vector???
>         Johnny
> --
> Johnny Billquist                  || "I'm on a bus
>                                   ||  on a psychedelic trip
> email: bqt at             ||  Reading murder books
> pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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