Communication between an input/output device and the microcomputer takes place through an interface. The interface converts the data from a form used by a device to a form acceptable by the other.
It must also adjust for speed differences between the processor and the input/output device. The interface circuits used in microcomputers correspond to the I/O control units of larger systems.
Two general types of the interface of microcomputer devices in use are:
Interface of microcomputer
- Serial interface, and
- Parallel interface.
Serial Port and Serial Interface
A serial port is associated with the serial interface and a serial input/output is connected to the PC through the serial port. The serial port is simple in concept; it uses one line to send data, another line to receive data, and a few lines to regulate the flow of data.
For its simplicity, the serial port is used to make a PC communicate with just about any device imaginable (modem, printer, plotter, etc.). Common uses for a serial port are with a mouse or modem. A serial port is not a very efficient way to transfer data. It can only send data in series, one bit of data at a time.
This inefficient data transfer, however, is acceptable for a mouse, which transmits so little data that speed is not crucial. The serial port is often referred to as an RS-232 port. Both 9-pin connectors are used as serial ports.
Parallel Port and Parallel Interface
A parallel I/O device is connected to the PC through the parallel port associate with the parallel interface. The parallel port has been synonymous with printer port since the early days of microcomputers.
A serial port sends data one bit at a time, a parallel port can send several bits of data across parallel wires simultaneously. A serial connection sends a single bit, a parallel port can send an entire byte. Some early printers and plotters used serial ports to communicate with printers.
But today, graphics and scaleable fonts are common in printer documents and they require that vast amounts of data be sent to the printer, making a parallel port the only practical choice.
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