semi-homemade micro

woodelf bfranchuk at jetnet.ab.ca
Mon Nov 14 18:59:53 CST 2005


Brad Parker wrote:

>Jim Battle wrote:
>  
>
>>The original PDP-8 took 10 clocks at 1 MHz to execute one instruction
>>    
>>
>
>  
>
Well that number now that I think about it is way off, from  memory 
speeds in the
PDP -8  Faq.  The handbook lists the pdp-8/e as 1.2 us for jump and 
operate instructions.
2.6 us for memory instructions.+1.2 us for indirect.+1.4 us for 
auto-indexed. A 5 mhz clock
looks to be used. I/O  seem to have a variable time but 2.6us is the 
general speed listed.

>really?
>
>I'm probably off, but at a cocktail party I would would have said that
>some instructions took 8 clocks (f0,f1,f2,f3,e0,e1,e2,e3) and some took
>12 (f0-f3, d0-d3, e0-d3).
>
>  
>
I downloaded a PDP-8 maintance manual  (pdf) once and give the full 
details of every time
state. The machines of that era of tightly coupled to the core-memory cycle.

>That's according to a recent look at the "blue book", but I may have
>misunderstood.  I did write up some verilog which uses those states and
>it seems to be (mostly) correct, but it's done all debugged yet.
>
>-brad
>  
>
PS.  Finds tinyfoot note.  PDP-8,PDP-8/I  1.5 us memory cycle. PDP-8/L 
1.6 us PDP-8/S 8us




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