[Coco] Assembler Question???

jdaggett at gate.net jdaggett at gate.net
Wed Sep 2 12:42:19 EDT 2009

To the list:

I have started looking at two FPGA cores for the 6809 in altering one of them to handle 
6309 opcodes and stumbled across a potential  issue. As far as I can remember the 
Motorola Freeware Assemblers treat subtraction as adding the 2's compliment of the 
subtrahend. Also I seem to remember that is how the internal workings of the MC6809 
is. There is actually no subtractor but the assemly code has the 2's compliment of the 
subtrahend and does addition. 

If this is so then, the ALU becomes simpler when doing a FPGA core.


More information about the Coco mailing list