Addressing the 8255
A1 A0 = 00 Port A ; IN, OUT 8 bits at a time
= 01 Port B ; IN, OUT 8 bits at a time
= 10 Port C ; IN, OUT 8 bits at a time
= 11 Control Register; Write ONLY!
PORT2A = 0224h ;Port A externally available
PORT2B = 0225h ;Port B externally available
PORT2C = 0226h ;Port C externally available
STAT2 = 0227h ;8255-5 # 2A / Status Register