4 Jan
2011
4 Jan
'11
1:45 p.m.
If I've understood the matter correctly the 11/73
can utilize 22 bits of
the Q-BUS but the 11/23 only 18 bits and that means that some cards are
18 bit only and others 22 bit only.
As I rememebr it, there's a signal on the Qbus (it has no Unibus
equivalent) which indicates an access to the I/O page. Properly designed
I.O devies (anything from DEC at lesst) use this signal rather than
decoding the upper address lines.
So any peripheral card which does not do DMA will work with the 11/23 or
11/73 processor.
With DMA cards, the stiuation is a little harder. The I.O card generates
the addess in during DAM. Older cards (the RLV11 is one, the RXV21 is
another IIRC) only generate 18 bits of address. They will work in a 22
bit system, but they can only transfer data to the bottom 128kW of
memory. Some OSes IIRC handles this fro you, they set up a buffer in a
suitable area of memeory and transfr the data there, Others have
problems. Later cards (RLV12 for example I think) gerneate all 22 bits of
DAM addrss and work fine with thr 11/73
-tony