PDP11 I/O page memory map

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu Mar 1 06:00:32 CST 2018

    > 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:


(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.


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