Explain I/O interface

An I/O interface is the hardware between the CPU/system bus and a peripheral device. It converts the signals and data format of the device into those of the computer and controls the transfer.

Functions of an I/O interface

• Speed matching: a buffer holds data because the device is much slower than the CPU.
• Data format and code conversion: serial to parallel and parallel to serial, and voltage level or code differences.
• Control and timing: issues the device commands and synchronises the transfer using status flags and handshaking.
• Device selection: decodes the address to find which device the CPU wants.
• Status reporting: tells the CPU if the device is ready, busy or in error.
• Error detection: detects errors such as parity errors.
• Interrupt generation: informs the CPU when the device is ready.

  CPU / system bus                       Peripheral
  +---------+     +----------------+     +--------+
  | Address |---->| Interface      |---->| Device |
  | Data    |<--->| Data reg       |<--->|        |
  | Control |---->| Status/Control |<----|        |
  +---------+     +----------------+     +--------+