Trying to get my RLV11 working

Ben Sinclair ben at
Wed Oct 28 11:15:43 CDT 2015

Hi Jerome, thanks for the info!

According to the Microcomputer Interfaces Handbook, my H9273 backplane
should be all ABCD. Am I correct in that I shouldn't have any problem
using the RLV11 in that backplane?

On Wed, Oct 28, 2015 at 11:29 AM, Jerome H. Fine <jhfinedp3k at> wrote:
>>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

Ben Sinclair
ben at

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