29 Jan
2010
29 Jan
'10
7:20 p.m.
Tony Duell wrote:
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
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