Department of Computer Scien

ce and Information Engineering

National Cheng Kung University, TAIWAN

HANEL

‰Examples 15-4 and 15-5

¾decode the A0 - A7 address bit

‰Examples 15-3 and 15-2

¾decode a portion of upper address A8 -A15¾this partial address decoding leads to what is called

address aliases

¾could have changed all x

’s to various

combinations of 1s and 0s ƒto come up with different addressƒthey would all refer to the same physical port

‰Make sure that all address aliases are documented, so that the users know what address are available if they want to expanded the system

PROGRAMMING THE 8255Address Aliases