Types of Interfaces

Interface are of two types they are:

Parallel Interface

A parallel interface transfers data in the form of one or more bytes in parallel to or from the device.

Assume a 16-bit, byte-addressable computer, where program controlled I/O is used with asynchronous of bus, and timing of bus transfers are some. The interface contains separate data buffers for input and output and there is one status register associated with each buffer. For an input operation, and word of data is transferred from the output device to registers and set to 1. When as soon as the ready signal is received, it enables the output gates corresponding to the addressed byte or word and placing its contents on the data lines. Also, the output signal accept is also set to 1. This constitutes the response of the interface to the read request issued by the CPU. As soon as the ready signal drops to 0, the accept signal is removed and all the bus is cleared. Note that when the buffer is addressed, the input status flag is reset to 0. This is essential in order to guarantee that each item of input data is read by the computer only once. An output operation proceeds in the same way, when the enable signal is set to 1. The clock input to the output buffer is set. This results in loading the buffer with the data on the data lines. At the same time, is set to 1 to indicate that the interface is ready to accept a new output transfer.

Serial Interface

A serial interface transmits and receives data one bit at a time.

A serial interface contains the same addressing and control circuit as the parallel interface, but with an addition controls for transferring data serially between registers and the I/O device. Here, a chip is used, which is an integrated circuit ship that contains all the logic circuit for the required parallel-serial conversion. The two registers and the status flags are included on the chip.

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