litwr wrote:
And anyway 6502+ would be much better because 6309 has a lot of bulky instructions, can use only 64 KB of memory, ...
...and the 65C816 is better still with 16 bit registers, 24 bit memory addressing, block copy instructions, stack relative addressing, fully relocatable direct page, support for high clock speeds (20 MHz if the rest of the circuit can handle it), etc.
You keep comparing apples (no pun intended) to oranges when you bring the 6800 MPUs into the discussion. The 6502's design was intended to eliminate the two most glaring weaknesses of the 6800, namely the lack of two index registers and the cost per piece (the latter is what influenced Wozniak into choosing the 6502 over the 6800). Obviously the 6502 greatly succeeded in that respect, as the home computer revolution was largely fueled by 6502 systems, not 6800 systems.
Comparison of the 6502 to the 6309 is only partially relevant, again apples to oranges—different MPUs with different intended "audiences." The 65xx family stands on its own, as is abundantly clear when one considers the countless millions and millions of 65xx MPUs that have been and continue to be used. Also, it is safe to say that the 6502 (and derivatives) is one of the most documented microprocessors in history. Only recently has the number of Internet search engine hits on "x86" exceeded the number of hits gotten when searching on "6502."
In my opinion, the 65C816 makes a better starting point for a homebrew computer than the 65C02 (or the much slower 6309), simply because it is a much more capable device, yet still adheres to the 65xx "philosophy" of a friendly bus structure, clean programming model and ready availability. One doesn't have to be concerned about 16 MB addressing to build a basic 65C816 system, as minus the bank latching circuitry, the 65C816 looks like a 65C02 as far as memory and I/O are concerned. It powers up in 65C02 emulation mode, which means it will run almost all 65C02 software without error. Once the programmer gets comfortable with the '816 he can switch to native mode (
CLC -- XCE) and tap into the enhanced capabilities. That is how I started with my POC units, and it worked out well for me.