[Coco] Re: wondering about 68k machines

[jdaggett at gate.net]

Kevin

The MC68000 first shipped in 1979. The MC6809 first shipped I believe in 1978. 
The external clock version, MC6809E, shipped first in 1979/80 time frame. The 
MC68000 first shipped in 1979. There  was an overlap in the time frame of 
development of both processor families. The 6809 was not so much a predicessor 
of the MC68000. 

The MC6809/09E were an improvement to the 6800. You have to realize that 16 bit 
processors were extremely expensive. This was the bridge between 8 and 16 bit 
processors. The 6809 had some 16 bit funtions like add and subtracts, compares 
and memory retrieval and storage. It had enough 16 bit operations as well as 8 bit 
operations that customers at that period could take advantage of and not have to 
invest in the cost of 16 bit processors. I really doubt that the design team and 
management ever thought that the processor would hang on in production until 
1990. 

ONe thing that Ritter mentioned in his Byte interview was that they did not want to 
have pnuemonics for every type of instrruction. Instead they felt the 59 base 
pnuemonics and post byte instruction did not require a programmer to remember 
say 42 different transfer possible pnuemonics. In many ways the 6809 simplified 
programming from the 6800. The MC68K was to address the true 16 bit world. 

james
  

On 10 Jul 2005 at 23:48, Kevin Diggs wrote:

Date sent:      	Sun, 10 Jul 2005 23:48:34 -0700
From:           	Kevin Diggs <kevdig at hypersurf.com>
To:             	CoCoList for Color Computer Enthusiasts 
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Subject:        	Re: [Coco] Re: wondering about 68k machines
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> How certain are you of this? I was thinking (i.e. just guessing) that
> the 6809 was a slightly newer design based on the following fact:
> 
>  Doesn't the 6809 have some indirect addressing modes that did not
>  show 
> up in the 68k until the 020?