6809 SBC

[CSquared]

Tony Duell wrote:
>> Having learned assembly language programming on the beautifully 
>> simple architecture and instruction set of the 6800, the Byte magazine 
>> article linked to below that I read when it was originally published 
>> really impressed me.  In the 6809 they made one of the earliest efforts 
>> I know of to really tweak an already great uP instruction set based upon 
>> an analysis of existing software: 
> 
> I found the 6809 to be by far the nicest 8-bit CPU I ever worked with. 
> The instruction set was simple and very orthogonal, the fact that you had 
> various relative addressing modes meant you could write truely 
> position-independant code, there were 2 stack points, and so on. Unlike 
> certain chips I could name, there were no major misfeatures that I came 
> across.
> 
> Of course the problem (as we all know) is that it came out too late. By 
> that tine everybody was using the Z80 or 6502. Oh well.
> 
> It always suprised me that hre BBC micro used the 6502 rather than the 
> 6809. By the time the Beeb was designed, Acorn had made a 6809 processor 
> board for their System machines, so they must have had experience with 
> the chip. THe Beeb is nice, but a Beeb with a 6809 processor would have 
> been something else :-)
> 
> -tony
> 
When I moved from the 6800 to the 6809 (in assembly language - *many* 
years ago) I was sort of astounded and at the same time very pleased by 
the way many of the little subroutines I had written for the 6800 became 
one instruction in the 6809.  I think it will always be my favorite 
8-bit CPU.  My only annoyance at the time was the fact that there was no 
way for the software to reset the companion UART chip, whose number I've 
completely forgotten by now.  6821 maybe???
Later,
Charlie Carothers