<in Q18 systems, right? They have to decode their CSR addresses, right? Ho
<can the same card work in both if Q22 compatibility requires decoding
<BDAL18-21 while in a Q18 backplane these fingers may be dangling or
<connected to something odd? Or is the I/O page where all the CSRs are

If you knew anything about Q-bus you'd know of one very important signal
and it's called BBS7.  The few non-conforming (mostly Q-16) cards don't 
use it.  It's used to signal all device CSRs that the address regardless 
of the Q-bus address width is one that is in the CSR or bank 7 range.
It saves the devices from having to decode the top 3-7 bits and makes the 
device independent of Q-bus address width.  It was implemented on Qbus 
starting with the LSI-11/03 (kd-11) the first/original 16 bit address 
version.

Also you have to know PDP-11 conventions and addressing to know all CSRs
are in the top 4kw in the 16 bit address space commonly known as bank 7.

<certainly do DMA, and they are listed as fully Q22-compatible. OTOH, RXV2
<and RLV11 are certainly for Q18. Since it's very unlikely that an RX01
<controller is newer than an RX02 one, it seems that RXV11 should work in 
<Q18 system too. What does it put out on BDAL18-21 during DMA to make bot
<systems happy?

RLV11 and RLV12 controllers both work in q22 or Q18, the difference is 
the RLV11 will only DMA in the lower 18bit address space.  The unasserted 
address lines default to 0000.  The RXV11 is not a dma device and works in 
all Q-busses (16, 18 and 22).  The RXV21 is a DMA device but only provides 
18bit dma addresses and also works in all Q-busses.  In the RX02 case that
18bit dma limit is rarely a problem as the media is only 512kbytes total.
Floppy transfers are generally on the small quantity of blocks level. 
Again the design of Q-bus takes care of unasserted address high order 
address bits.  I have successfully used RLV12 and RXV11 and 12 in 
microvax-II systems.  The RLV11 would work but it requires a special 
CD interconnected backplane (m9273, incompatable with microvax) as it's 
a two board set.

Get a copy of the PDP-11 microcomputers and memories books for Q and U
bus it's in there.  I still have the first copy with the 11/03 cpu I got 
back in '79.  


Allison