On 10/25/2013 05:23 AM, Jerome H. Fine wrote:
This is possible, but seems VERY unlikely with just
a 4 slot backplane. As far as I understand, in order
to be useful to support an RL controller, at least 2 slots
must be wired as ABCD.
I've got an original pdp11/03 in a four-slot backplane,
_all_ the slots
are Q18/Q18 serpentine. The RLV12 (quad width) lives in slot 3, the
system works great.
The BA23 box has the first
three slots as ABCD and the other five slots as ABAB,
so the concept is possible. Having two ABCD slots also
supports PMI memory with the memory being placed in
slot 1 and the CPU in slot 2, but that requires at least
a quad M8190 CPU card.
> It gather that I insert the CPU in 1AB, then rather than putting the
> next card in 2AB, I would place it in 1CD. Next would be 2CD and so
> on ,snaking down the line. Is this correct?
Assuming the bus is in fact QQ/QQ
serpentine, yes.
> While this is all fine for dual cards, but how
does this configuration
> handle quad cards?
As long as quad-width cards don't mess about on the
right-hand side
connectors (most of them don't) you can use any quad-width slot, whether
its wired QQ/CD or QQ/QQ.
With an M8186 to start, the BDAL17-20 lines should be
either unconnected (for an 18 bit backplane) or ONLY
connected to each other (for a 22 bit backplane).
Just a clarification, the
high-order four address lines are BDAL18-21...