Even more PDP-8/A weirdness (was: Re: PDP-8 diagnostics

Charles charlesmorris800 at centurytel.net
Sat Sep 12 12:08:09 CDT 2015

>So, either something is corrupting the bus, or the memory is bad.
>Correct me if I'm wrong, but if I got this right, you wrote the boot
>code by hand into memory, single-stepped it, and after a while, you had
>bad contents in memory.
>Now, execution here would only be reading from memory, and not writing
>to it. Furthermore, this is MOS, so it does not get rewritten on reads.
>That would, to me, suggest that the memory board is the problem.
>Do you have any other memory board around?

I mistyped while doing many things at once.
(It appears that the memory does NOT change while single stepping through it 
by hand. Fortunately.)
See my update - reseating the ROMs fixed the boot corruption problem.

I am not sure if the 32K SRAM board actually reads and rewrites - it does 
not do so internally, it's just SRAM and a couple of bus buffers.
Whether the 8/A memory cycle does rewrite each time or not, I don't know.

Now I've got yet another RL02 (maybe) problem to chase down...

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