Communication with CPU requires

•          I/O addresses

•          IRQs

•          DMA channels

•          memory addresses

               I/O Addresses

•          All devices connect to the address and data buses

•          How does the CPU signal it wants to talk to a specific device?

•          How does a device know the CPU is talking to it?

•          Each device has a unique code called an I/O address

•          CPU uses I/O addresses to identify which device it’s communicating with

                 I/O Addresses

•          Keyboard uses I/O addresses 0060 and 0064

•          Although a device can have more than 1 I/O address, no 2 Devices can share an I/O address in the same PC

•          I/O addresses are written in hexadecimal

•          Hexadecimal is a convenient shorthand way to describe a series of binary values

•          I/O addresses are hard coded into the device

•          Sometimes you can select a specific I/O address by moving a jumper

•          IBM list of I/O addresses

•          E.g. 03F0-03F7 = Floppy Controller
03F8-03FF = COM1

•          Original list is still supported

•          New devices have to use unallocated I/O’s