> On Mar 8, 2016, at 3:44 PM, Mike Ross <tmfdm...@gmail.com> wrote:
>
>>> ...
>>
>> No, it will only have 128KW. Since it’s a single FRAM part, I’m not going to
>> try and “stock” different flavors (especially since I’ll be having the boards
>> assembled at the board house).
>
> But you will do something to allow memory to be switched in and out? I
> presume this thing wouldn't work in an 11/20 unless it was strapped
> back to 32KW? Or will the 11/20 be happy and simply ignore the
> unaddressable memory beyond 32KW?
The Unibus has 18 address lines. This should work so long as the memory
doens't respond to I/O page addresses (the top 4kW of the address space).
That's a requirement for any Unibus memory on any PDP11. The difference
between 11/20 and 11/05 vs. the others is that the lack of MMU means that the
CPU can't generate addresses in the range 28 to 124 kW. (I/O devices can,
though, which would be rather interesting.)
paul
