yet another pdp-11 in fgpa

[Don North]

On 6/22/2010 11:43 AM, Don North wrote:
> On 6/22/2010 12:34 AM, E. Groenenberg wrote:
>>>
>>> Johnny is right, the 11/74 option was a multiboard set (just like the
>>> FPP option) that could be plugged into the new 11/74 backplane (which
>>> was an 11/70 backplane with all the CPU and FPP slots pushed down by
>>> four to make room for the CIS option in the first slots).
>> How was this achived? By reducing the Massbus card space by 4 boards
>> so 3 interface sections were available? Or by redesigning the processor
>> in such a way that there were less boards needed?
>>
>> Ed
>>
>
> Removed one of the MASSBUS controllers.
>
> The CPU board set was essentially the same, slot for slot. There were 
> several boards that needed rev/ECO to provide hooks for the CIS 
> option, but all in all these were minor updates and were backward 
> compatible.
>
> IIRC the main change was to add additional microcode to the base 11/70 
> microengine (from 256 to 512 words) by doubling the PROM bit density. 
> This code did all the base instruction dispatch and operand fetch for 
> the CIS unit.
>

BTW you can read about it here:

http://www.bitsavers.org/pdf/dec/pdp11/1174/Prelim_KB11-E_Diffs_Aug78.pdf

Don