[Coco] Interesting thoughts on the HD6309

[jdaggett at gate.net]

Interesting find. 

Again as I was searching the patents on the US Patent Database, I cam across a 
Motorola Patent that also references other patents by RCA and Honeywell. I think 
I better understand  the reason the hidden feature of the 6309 when it does an 
instruction fetch while executing a previous instruction remained unpublished. It 
seems that Motorola did a patent on this feature but also there were 9 previous 
patents on this same subject. 

 Microprocessor having instruction fetch and execution overlap 

It more appears that Hitachi had implemented it in the 6309 and just before 
release of the product  info, their lawyers determined that any info about this 
mode would violate not just a Motorola patent but maybe also ones by RCA and 
Honeywell also. It is easier to fight one company in a patent infringement suit. To 
fight three or even four companies is far to difficult and costly. 

It looks as if Hitachi could not find a way around the ten patents and thus never 
deleted the feature. Instead they were silent about it and hoped no one would find 
out about it. By the time the community had found out about this feature,some of 
the original patents had expired and Motorola's was also near expiration. Also no 
one decided to persue infringement because Hitachi failed to document this 
feature and not use it as a selling point or an invention of their own. 

james