Browse Definitions :

serial communications interface (SCI)

What is a serial communications interface (SCI)?

A serial communications interface (SCI) is a device that enables the serial exchange of data -- that is, one bit at a time -- between a microprocessor and peripherals, such as printers, external drives, scanners and mice. In this respect, it is similar to a serial peripheral interface.

SCIs also enable serial communications with another microprocessor or with an external network. Motorola coined the term serial communications interface in the 1970s. In some applications, it is known as a universal asynchronous receiver/transmitter, or UART.

Diagram of how a serial communication interface works
With a serial communications interface, data travels between a sender and receiver in one direction, one bit at a time.

How does an SCI work?

An SCI contains a parallel-to-serial converter that serves as a data transmitter and a serial-to-parallel converter that serves as a data receiver. The two devices are clocked separately and use independent enable and interrupt signals.

SCIs operate in a non-return-to-zero (NRZ) format, which is a form of digital data transmission in which the binary low and high states are transmitted by specific direct current voltage. They can function in half-duplex communication mode, using only the receiver or only the transmitter, or in full-duplex mode, using the receiver and the transmitter simultaneously. The data speed is programmable.

Descriptions of various communication modes
Serial communications interfaces can function in either half-duplex or full-duplex mode.

Serial vs. parallel interfaces

Serial interfaces have some advantages over parallel communications interfaces. The most significant is their simpler wiring. In addition, serial interface cables can be longer than parallel interface cables because there is less interaction, or crosstalk, among the conductors in the cable.

The term SCI is sometimes used in reference to a serial port. This is a connector found on most PCs that's intended for use with serial peripheral devices.

Special bits of data, such as a start bits and stop bits, are used to manage serial communications before data transfer occurs and after it has concluded. Other bits are used to transmit data and to receive data. Data transmission is largely asynchronous serial communication, in that it occurs only one message at a time, as opposed to synchronous transmission, where multiple data transfers can occur simultaneously in both directions.

Diagram showing the difference between synchronous and asynchronous communication
Data transmission using a serial communications interface is mostly asynchronous.

Pros and cons of serial communications interfaces

Advantages of using serial data communications interfaces include the following:

  • Have fewer wires.
  • Cost less than other devices.
  • Support long-distance communication between devices.

There are drawbacks to using SCIs:

  • Require data to be sent to be well organized.
  • Need device controllers to manage all data communications with peripherals and embedded systems.

Learn more about synchronous vs. asynchronous communication.

This was last updated in May 2023

Continue Reading About serial communications interface (SCI)

  • CSU/DSU (Channel Service Unit/Data Service Unit)

    A CSU/DSU (Channel Service Unit/Data Service Unit) is a hardware device about the size of a modem. It converts a digital data ...

  • data streaming

    Data streaming is the continuous transfer of data from one or more sources at a steady, high speed for processing into specific ...

  • secure access service edge (SASE)

    Secure access service edge, also known as SASE and pronounced sassy, is a cloud architecture model that bundles network and ...

  • recruitment process outsourcing (RPO)

    Recruitment process outsourcing (RPO) is when an employer turns the responsibility of finding potential job candidates over to a ...

  • human resources (HR) generalist

    A human resources generalist is an HR professional who handles the daily responsibilities of talent management, employee ...

  • employee lifecycle

    The employee lifecycle is a human resources model that identifies the different stages a worker advances through in an ...

Customer Experience
  • Adobe Experience Platform

    Adobe Experience Platform is a suite of customer experience management (CXM) solutions from Adobe.

  • virtual assistant (AI assistant)

    A virtual assistant, also called an AI assistant or digital assistant, is an application program that understands natural ...

  • inbound marketing

    Inbound marketing is a strategy that focuses on attracting customers, or leads, via company-created internet content, thereby ...