More PDP 11 hacking (help!)

From: Vintage Computer Festival <>
Date: Tue Feb 8 18:10:14 2005

On Tue, 8 Feb 2005, Pete Turnbull wrote:

> Interesting -- this is an 11/23, yes? It presumably has 64KB of


> memory, or more. However, what a program can see is at most 56KB of
> addresses, and the remaining 8K is the I/O page. When you look at
> 165426 with ODT, you see the physical memory, but when the processor
> does it, any address above 157777 is mapped to the I/O page. To see
> what the processor would see while it's executing the bootstrap, you
> would need to look at 17765426. Unless it's one of the early KDF11-As,
> with only 18-bit ODT, in which case you should look at 765426 (17765426
> would actually give the same result, though, because of the way ODT
> works).

Ok, cool. I'll examine this tonight.

> If it helps, I can give you an annotated copy of the RXV21 bootstrap.
> I've posted it here before, but I can do it again. I've got other
> noddy toggle-in programs, for example one that prints out all the valid
> addresses in the I/O page, and I have a listing of the standard
> addresses and what uses them.

All this information would be highly useful to me, and posting it here to
the list will probably help someone else down the road, so please do post

I'm actually looking forward to digging in to PDP11 machine code (I've
been a 6502 junkie all my life so something new [and old] will be a
welcome change).


Sellam Ismail                                        Vintage Computer Festival
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Received on Tue Feb 08 2005 - 18:10:14 GMT

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