[Coco] MC6809 Inards

[jdaggett at gate.net]

On 5 Oct 2006 at 0:04, KnudsenMJ at aol.com wrote:

> In a message dated 10/4/06 2:32:04 PM Eastern Daylight Time,  
> jdaggett at gate.net writes:
> 
> >I  did  not follow every reference patent, but if one did then one maybe led 
>  to 
> >those patents. I did not specific search on the PDP-11.  
> 
> OK, understood.  I suspect that if one did search on patents specific  to the 
> PDP-11 (provided that DEC listed them that way, maybe not; specific  products 
> rarely appear in patent briefs), you would find a treasure trove of  great 
> ideas, many used in every CPU since then.
> 
**************

Mike 

Every patent from 1976 to present can be searched under about 16 different sources. 
One being the Title of the patent, the actual patent number, the actual day it was filed or 
the issue date. I limited my search to the assignee and the dates issued during a 
specific year. That often limited the search results to 300 to 600 to investigate at a time.

 
> >The  MC6800 and offspring use an incrementer linked with the PCR and a 16 
> bit  
> >temp register. There is a patent that does describe how to do  precharge 
> from a 
> >carry. Looks as if this does the actual  increment/decrement by one or by 
> two. 
> 
> 
> Every CPU has to auto-increment its PCR. I built a computer out of TTL DIPs  
> at Bell Labs that had a set of adder chips whose only function was to 
> increment  the PCR.
>  
> But the PDP-11 could auto-inc/dec the stack pointer reg, and I think any of  
> the general-purpose regs, which could serve as index registers or  
> accumulators.
> The 6809 can auto-inc/dec X,Y, SP, and of course PC.
>  
************

Only the Pointer registers are auto pre/post incremented/decremented (X,Y,S and U). 
The PCR is decremented/incremented is not exactly. The PCR is not dec/inc until after 
instruction fetch and decoded I believe. 


james