1. Input/Output

2. Objective Issue commands to the devices Catch interrupts Handle errors
Provide user interface

3. I/O Device Classification
Based on data flow :
Block device
Save and transfer data as blocks, example : disk, tape, CDROM, optical disk
Character device
Save and transfer data as character, example : terminal, printer line, mouse

4. Basic Concept I/O device is connected to computer by port.
Communicate with processor and other devices by bus.
Communication between devices and processor – 2 methods – memory mapped and direct I/O instruction.
Processor repeatedly checks for available access to devices – polling
I/O Device tells processor for available access – interrupt

5. Register for I/O Port
- Data-in register - Data-out register - Status - Control

6. Bus Structure

7. Processor – I/O Communication
Direct I/O instruction
each control register is assigned an I/O port number, an 8- or 16-bit integer. Example : IN REG,PORT (read), OUT PORT,REG (write)
Memory mapped
I/O registers are part of the regular memory address space,
Direct I/O instruction
Memory Mapped

8. Interrupt Because of : Available to be accessed Output Error Steps :
Controller sends interrupt signal using interrupt request line, detected by processor
Processor saves the state of process and identify interrupt
Control transfer to interrupt handler
Processor continues its job

9. Direct Memory Access