IO Interfaces and Bus Standards

1. IO Interfaces and Bus Standards

2. Interface circuits • Consists of the cktry required to connect an i/o device to a computer. • On one side we have data bus signals for address, data and control. • On the other side we have a data path with its associated control to transfer data between the interface and the i/o device. This side is called port. • Parallel port • Serial port

3. Functions of I/O interface ckt • Provides a storage buffer for at least one word of data • Contains status flags that can be accessed by the processor to determine whether the buffer is full or empty • Contains address decoding cktry to determine when it is being addressed by the processor. • Generates the appropriate timing signals required by the bus control scheme. • Performs any format conversion that may be necessary to transfer data between the bus and the i/o device.

4. Parallel port • Multiple data path is used. • Short distance • Higher speed • Usually a parallel port transfers a byte at one time.

5. Input Interface ckt • Any input interface must use three state logic device. • Slave ready is set when either read status or read data is present. • Any read operation is performed at master ready signal active. • LSB address bit is used to identify the status read or data read.

6. Output interface ckt • Output is latched • A0 is used to select either status or data. • Handshake signals are generated: idle, valid

7. Combined Input/Output ckt • A0, A1 2 bits are used to select status or data registers