Trying to get my RLV11 working

Jerome H. Fine jhfinedp3k at
Wed Oct 28 11:29:15 CDT 2015

 >Noel Chiappa wrote:

>    > From: Ben Sinclair
>    > I'm trying to get my RLV11 working
>Oh, I was going to mention this about the RLV11 - it's a Q18 device. So it
>_probably_ won't work in a system with more than 256KB of memory (which you
>don't, at this point, have, though). It would all depend on the OS, whether
>it understood that it couldn't DMA to anywhere above 256KB. (The controller
>should work OK in a Q22 system - it just won't drive the high address lines,
>so they will go to 0 - but it just won't be able to DMA to high memory.)
The rest of Noel's reply agrees with my information, so
I will not comment.

However, just to place another option on the table, here
is that option which I observed around 20 years ago.

I was looking at some PDP-11 hardware in a BA23 box
and I noticed it had an RLV11 in slots 2 and 3.  For those
of you who don't know the details, the first 3 slots are
ABCD and the other 5 slots are ABAB.  Of course, all
of the slots in a BA23 box are Q22.

The key point is that an RLV11  MUST be placed into
a pair of ABCD slots, probably adjacent.  Since the
CPU board in this example was in slot 1 in the BA23
box, there were only 2 ABCD slots available in any
case.  NOTE that placing an RLV11 in two ABAB
slots will probably ALWAYS result in a release of the
magic smoke which activates all computer boards (at
least it did when I performed the experiment).

One key point to understand is that although the RLV11
can't perform DMA to memory above 256 KB, that
does not mean that the system can't have more than
256 KB of physical memory.

If there is anything that I have omitted by way of a
full explanation, please ask.

Jerome Fine

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