[Info-vax] RB730 Integrated Disk Controller (R80/RL02) usable with VAX-11/750?

[SeanOBanion]

On May 5, 9:57 am, Johnny Billquist <b... at softjar.se> wrote:
> On 2011-05-05 07:02, Bob Koehler wrote:
>
> > In article<ipt5am$d6... at Iltempo.Update.UU.SE>, Johnny Billquist<b... at softjar.se>  writes:
>
> >> That's what the Unibus Map is there for. The Unibus map sits between the
> >> Unibus and the memory, and remaps DMA from the Unibus into the larger
> >> address space of the memory bus. Same both on the 22-bit capable PDP-11s
> >> and all VAXen. The exact details of the Unibus map differs between a
> >> PDP-11 and a VAX, though, but the principles are exactly the same.
>
> >     Too me, that map is part of the memory subsystem.
>
> The Unibus map is the very important piece that maps Unibus addresses to
> memory bus addresses for DMA. As such, is it a part of the memory
> system, or the Unibus? It sits on both...
>
> Either way, it is absolutely necessary in order to have DMA from the
> Unibus work on a machine where the memory does *not* sit on the Unibus.
>
> On lowly PDP-11 models, where the CPU only address 18 bits (or less),
> the memory really sits on the Unibus, and DMA can be performed directly
> there, and memory is responding to Unibus signals. This is (obviously)
> very different from when you have machines with a Unibus map.
>
> Thus, on any VAX, the memory does not sit on the Unibus, and the Unibus
> is only used as an I/O bus. As someone else mentioned, the MicroVAX I is
> the only design where you really only have one bus, the Q-bus in that
> case. The uVAX I therefor is limited to the physical address space of
> the Q-bus (which is 22 bits), and DMA can be performed directly between
> peripherials and memory, which both sits on the same bus.
>
> A short additional note. On PDP-11s the Unibus map is located in
> different places depending on model. For the 11/44 it's in the MMU. The
> 11/70 have it along the cache. The 11/84 and 11/94 have the Unibus map
> on the Unibus adapter which is a separate card on those machines.
> For all of them, DMA from the Unibus "speaks" (that is, do all the
> Unibus handshaking and signalling) with whatever have the Unibus map.
> And the Unibus map in turn then "speaks" with the actual memory.
> When the CPU speaks to memory, the Unibus is totally unaware, and
> remains quiescent.
> (For a machine like the 11/70, and VAXen, when devices not on that
> Unibus speaks to memory, the Unibus is also quiescent.)
>
> So no, the memory is *not* on the Unibus. Memory can exist on the
> Unibus, and do so for 18-bit PDP-11 models, and that is obviously very
> different.
>
>         Johnny
>
> --
> Johnny Billquist                  || "I'm on a bus
>                                    ||  on a psychedelic trip
> email: b... at softjar.se             ||  Reading murder books
> pdp is alive!                     ||  tryin' to stay hip" - B. Idol

Yes, that does make sense, and fits what the doc's seem to say.
So my recollection / understanding of what was done to the 730 in
college must be wrong.

For the UDA50 version of the 730, I have to wonder if the UDA50
displaced some of the memory cards in the system box, because the
memory limit went from 5MB for the IDC version down to 3 MB.
Or at least did so in the factory version, but I can't tell if the
UDA50 could go in the expansion box (H9642-DH)


Thanks!
Sean