Memory map of original 810 disk drive

0000 - 007F  WD1771
0080 - 00FF  RAM
0100 - 01FF  RIOT RAM (twice)
0200 - 027F  WD1771 (mirror)
0280 - 02FF  RAM (mirror)
0300 - 03FF  RIOT REGS
0400 - 047F  WD1771 (mirror)
0480 - 04FF  RAM (mirror)
0100 - 01FF  RIOT RAM (twice, mirror)
0600 - 067F  WD1771 (mirror)
0680 - 06FF  RAM (mirror)
0700 - 07FF  RIOT REGS (mirror)
0800 - 0FFF  2316 os rom
