MEM11 Status Update

Johnny Billquist bqt at
Tue Jan 20 13:21:10 CST 2015

On 2015-01-20 18:04, Noel Chiappa wrote:
>      > From: Henk Gooijen
>      > but RP11 will never be possible, isn't that MASSBUSS!?
> Maybe you're thinking of the RH70, the MASSBUS <-> PDP-11/70 memory bus
> interface? But there was also the RH11, a MASSBUS <-> UNIBUS interface, which
> supported all the same devices (RP04-6, etc) as the RH70, but plugged into a
> UNIBUS. (The two were programming-wise almost identical, the RH70 had an extra
> register for the extended memory address bits, plus a 'CSR3'.)
> But I was speaking of the RP11, a UNIBUS interface for the RP03 (different
> beast from the RH11, although very similar).


One also needs to remember that the Massbus is a pure I/O bus. It's 
never a CPU bus. So you always needs to have a bus adapter if you are 
hooking up a Massbus drive to a machine. And of course, from the CPU 
point of view, you then talk to the bus adapter.

So really, emulating any Massbus device on a PDP-11 is not a problem. 
You essentially emulate the Massbus adapter, and whatever sits behind that.

And yes, for PDP-11s you had the RH11 that was the adapter, except for 
the 11/70 which used the RH70. Software downwards compatible, but the 
RH70 is more capable, in that it can do direct DMA to the whole memory 
space of the 11/70, without using the Unibus map.
It's also a whole lot faster than the RH11, which means it can run some 
devices that the RH11 did not support.
RP07, RM03, RM05 are the ones that comes to mind.
Probably also the TU78.


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