Serial Communications Interface in Microprocessors

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In microprocessors and microcontrollers, communication among different devices plays the most vital role. There are two main types of communication methods used in these systems: serial communication and parallel communication. In most microprocessors and microcontrollers, serial communication is the most widely used communication method.

Serial communication between microprocessors and other devices requires an interface, which is termed as Serial Communication Interface (SCI). SCI is well known for its simplicity and efficiency. Because of these features, it is used in a wide range of applications, from simple data collection systems to complex industrial automation systems.

In this chapter, we will have a discussion on SCI, its types, advantages, disadvantages, and applications.

What is Serial Communication?

In microprocessor technology, serial communication is defined as a type of data communication method in which data is transferred bit-by-bit i.e., one bit at a time. Hence, serial communication is a sequential method for data transmission over a communication channel or microprocessor bus.

This communication method is most widely used for long-distance communication. Due to enhanced signal integrity, simplicity, and data transfer speed, serial communication is also used in microprocessor and microcontroller buses.

What is Serial Communication Interface (SCI)?

Serial Communication Interface or SCI is a type of communication interface used for transmitting information in a serial or sequential manner between two or more devices.

It provides a way of transferring information bit-by-bit over a single channel. In other words, it allows to send one bit at a time over a communication channel like a microprocessor bus.

SCI makes use of two combined signals for communication, one for transmission and another for reception. SCI is most commonly used in microprocessor- or microcontroller-based system to provide their communication with peripherals.

How does Serial Communication Interface (SCI) Work?

Serial communication interface or SCI uses a parallel-to-serial converter which acts as a data transmitter and a serial-to-parallel converter which acts as a data receiver. Both devices are clocked separately and makes use of independent enable and interrupt signals.

Serial communication interface works in a NRZ (Non-Return-to-Zero) format which is a type of digital communication. In NRZ format, the binary low and high states are transmitted using a specific DC voltage.

Types of SCI

Serial communication interface can be broadly classified into the following three main types −

• Simplex SCI
• Half Duplex SCI
• Full Duplex SCI

Each of these types of SCIs are explained below in detail.

Simplex SCI

Simplex serial communication interface is one in which one-way of signal transmission takes place. It has a definite sender and receiver, where the receiver can not send single back to the sender. Simplex SCI provides a simple and efficient communication.

The block diagram of the simplex SCI is shown in the following figure.

It has the following key components −

• Sender − It is a device which sends data.
• Communication Channel − It is the medium through which data travels from sender to the receiver.
• Receiver − It is a device that receives and processes data transmitted by the sender.

Half Duplex SCI

Half duplex serial communication interface is a type of serial communication method in which only one communication channel is used for both data transmission and reception. But the transmission and reception cannot take place at the same time.

The block diagram of half-duplex serial communication interface is shown in the following figure.

It has the following main components −

• Sender − It is a device which sends data or information.
• Communication Channel − It is the medium either wired or wireless which carries data.
• Receiver − It is the device which receives and processes the data sent by the sender.

Full Duplex SCI

Full duplex SCI is a type of serial communication interface which allows for data transmission and reception at the same time. Hence, it allows for bidirectional communication. The block diagram of the full duplex serial communication interface is depicted in the following figure.

It also has same components as the simplex and half-duplex SCI to perform transmission and reception of data.

Advantages of Serial Communication Interface (SCI)

SCI offers several advantages, some key of them is given here −

• Serial communication interface is easy design, implement, and use.
• Serial communication interface is cost-effective.
• SCI is highly versatile, hence it can be used in various applications.
• It is one of the best options for long distance communication.
• Serial communication interface provides ability to identify errors in data transmission.

Disadvantages of Serial Communication Interface (SCI)

Despite numerous advantages, SCI also has certain disadvantages which are given below −

• It is a slower method for data communication.
• SCI has a limited data transmission size, typically 8 bits at a time.
• It has asynchronization issues. Thus, for reliable and effective communication, SCI requires precise timing.
• SCI uses start and stop bits that add data overhead.
• SCI provides only error detection facility, but it does not support error correction.

Applications of Serial Communication Interface (SCI)

Serial communication interface finds its use case in various applications. Some of the common are listed below −

• In embedded systems, SCI is used for providing communication between microprocessor/microcontroller and peripherals like sensors or IO devices.
• In computers, SCI is used for enabling communication between microprocessor and other devices like keyboard, mouse, printer, etc.
• SCI is also used in industrial automation systems for data exchange between PLCs and sensors.
• Serial communication interface finds its use in remote monitoring and control systems.
• In modem, serial communication interface is used for transmitting data over telephone lines.
• Serial communication interface is also used in GPS systems for transmitting data from receivers to other components.
• SCI is also used in medical monitoring devices.

Conclusion

The Serial Communication Interface (SCI) plays an important role in modern microprocessor technology. It allows devices to exchange data with reliability and efficiency. SCI is preferred in a wide range of systems because of its easy implementation, versatility, and efficiency.