PDP11 I/O page memory map

Douglas Taylor dj.taylor4 at comcast.net
Thu Mar 1 13:43:37 CST 2018


Thanks for the exact info I was looking for!  I knew there was a text 
listing of the addresses and what devices occupied those addresses.  
Going thru the manuals one by one was way too tedious.  Thanks for 
explaining the 'bank switching' that is done to accommodate the larger 
boot roms.  Suspected that was going on but didn't really know.

I'm curious because I have an MXV11-AC without the boot rom, however it 
does have another OEM rom there that I could reprogram with the standard 
bootstrap.  This led to the question I posted.


On 3/1/2018 7:00 AM, Noel Chiappa via cctalk wrote:
>      > From: Douglas Taylor
>      > Is there a document that describes the bank 7 memory page and what
>      > addresses are reserved for what?
> Here's one I collated from a large number of DEC manuals:
>    http://ana-3.lcs.mit.edu/~jnc/tech/pdp11/UNIBUS_Registers.txt
> (Ignore the name, it applies to QBUS machines too.)
>      > bootstrap is reserved for 173000, how many words are allowed there for
>      > this?
> Well, the space from 773000-773776 (UNIBUS and Q18 - add '17' to the front
> for Q22) is used for ROMs, and is the most common; 173000 is of course the
> location QBUS processors can be configured to jump to on power on. 765000-776
> in also used for some (e.g. M9301's).
>      > How do the more complicated bootstraps, e.g. microPDP11-53, accommodate
>      > this limitation?
> Bank switching; e.g. the BDV11, KDF11-B have a 'page control register' at
> 777520 which says which block of ROM is mapped into the 773000 block.
> Interestingly, the DEC standard ROMs for the BDV11 and KDF11-B _don't_ copy
> all the contents down to real memory, and run from there - the code is
> divided into 'pages', only one of which is mapped in at a time, and it's
> executed from the ROM.
> 	Noel

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