Continuing PDP11 saga

From: Tom Leffingwell <>
Date: Wed Jan 9 17:19:27 2002

        I think I finally get the picture on the addressing...However,
that raises two more questions. If my program is trying to talk to a
22-bit address, and I have 18-bit addressing, will it not work, or will it
be converted? Also, if my backplane becomes 22-bit (by replacing it or
adding the jumpers for the other 4 bits) does everything automagically
change to 22-bit, or do you change a jumper on the M8186, or on the MSV11,
or both?



On Wed, 9 Jan 2002, Pete Turnbull wrote:

> Well, if you're using 18-bit addressing -- which you must be if the DRV11-B
> responds to 772410 rather than 17772410 -- then all the I/O addresses begin
> 77.... rather than 17.... 17.... in ODT would address the memory. I/O
> addresses are often given as 17.... for older QBus devices, because the
> original LSI/11 used 16-bit addressing. You have to mentally add two or
> six more '1's on the front for an 11/23 or later processor.
Received on Wed Jan 09 2002 - 17:19:27 GMT

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