On Thu, 26 Jul 2012, aiiadict@gmail.com wrote:There were two 6809 boards, the other one I can't remember the name of. The other one ran Flex, which I think started with the 6800 (or perhaps a simpler operating system with a different name was the beginning), and was avaailable for the 6809 "mainframes" like the GImix and the SWTP. It also ran on the Radio Shack Color Computer. It was a fairly traditional operating system, a means of loading things, I seem to recall one could run Color Computer programs under Flex with minimal modification.On Thursday, July 26, 2012 4:25:49 PM UTC-7, Alex Freed wrote:Just finished the page http://alexfreed.com/FPGApple/Mill6809/6809_board.htmlWhat runs on the 6809 for the apple II? What is OS9? Screenshots from anyone? Were there commercial softwares for this coprocessor?
The MC6809 had a *peach* of an assembly language!!! There was an EXG instruction that could swap the contents between pretty much any two like-sized registers. One instruction. There were *two* stacks, and user and system stack. Two stack pointers. There was a PC-relative instruction that used the regular one-byte offset... and also instructions that used a longer offset. Push and Pul (pop) instructions were followed by a byte which had a bit set for which registers to push on or pop off the stack. Yes, and the 8x8 unsigned multiply... so you could use the instruction to write routines to multiply larger numbers.
Also, instead of zero-page instructions... the 6809 had *direct* page instructions. Zero-page instructions had a one byte address and the upper byte of the address was assumed to be zero. Direct page instructions had a one-byte address, and the upper byte of the 16-bit address was provided by a "direct page register". By changing the contents of the direct page register, you could move the direct page around in memory. And there were *two* 16-bit index registers. The A and B 8-bit accumulators were considered combined as one 16-bit register for things like a double add from memory.
-- numerist at aquaporin4 dot com