System05 - VHDL 6805
As a matter of stepping stone to the holy grail of designing
a MC6809 to run Flex, I have attempted to code a 6805. The 6805
only has one 8 bit accumulator and one 8 bit index register. Unlike
the Micro8 design it has a 5 bit stack pointer in the base page,
sitting at $007F and working down to $0060. Note that as of 6:53am
on September 19th 2002 it is totally untested and is very unlikely
to work. It does compile under ISE Web Pack 4.2, although generates
a few warnings. I have not implemented a proper timer module, and I have
to change the memory map for the ROM and I/O. Also the ROM code is probably
totally wrong.