PDP11 M9301-Yx ROM dumps

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu May 12 16:17:15 CDT 2016

Re: PDP11 M9301-Yx ROM dumps
    > From: Mattis Lind

    > I checked the contents in the machine versus your listing.

And now that I think of it, I wonder if the ROM in the board I dumped had any
errors? I have two, I should dump the other one and compare - but I forget
which one I dumped, and I fried one of them! :-(

The board did 'work', but I only used the console emulator, and the serial
line loader, so there might be an error elsewhere (e.g. in one of the disk

    > Two locations have the high bit set for some reason, 165020 read 100501
    > and 165032 reads 106303.

Well, the second is definitely wrong; not sure about the first, I'd have to
figure out what it's doing with that data word.

    > Trying to run halts the machine with 165102 in the front panel.

That's odd, that doesn't make any sense.

    > Single stepping it it will step to 165106 but become non-responsive
    > with the lights at 165106.

Hmm, does that mean that it actually froze at 165102, or at 165106? (I.e. is
the display the address of the current instruction, or the next one?)

    > I think this is because it had a bus fault.

That shouldn't freeze the machine - unless you had a double bus fault (i.e.
trying to push and old PS/PC, and the SP is gubbish). Try loading the SP with
the address of some working memory before you start the test, and see what
happens. You might also deposit 6/0/12/0 in locations 4-12, so that if it
does see an illegal instruction or NXM, it will just halt.

    > So for now, it is not necessary with more disassembly. Unless you have
    > som spare time of course.

Well, I'll keep working on it anyway.

    > You don't have a dump of the PROMs in Intel HEX?

No, but I do have a un-annotated dump in octal. Can you point me at a
description of Intel HEX format, so I can whip up a converter program? (Which
will also take an array of PDP-11 words, and split it up into the 4 different
ROM chips, since each word is spread across all 4 chips.) I already have a
program to read my octal dump things, so I'll just have to tweak that a bit.

I'm going to need to start blowing ROMs soon (including some sets of 9301-YF
PROMs, for the one I zorched), once I get my 29B hooked up, so I might as
well start with this...


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