Programmable Peripheral Devices

Introduction

Programmable peripheral devices play a crucial role in microprocessor systems by enabling data communication and input/output (I/O) operations. These devices are designed to perform specific functions and can be programmed to meet the requirements of various applications.

In this article, we will explore the different types of programmable peripheral devices commonly used in microprocessor systems and understand their features, modes of operation, programming techniques, and real-world applications.

General Purposes Programmable Peripheral Devices (8253)

The 8253 programmable interval timer is a widely used peripheral device that provides timing and counting capabilities in microprocessor systems. It consists of three independent counters that can be programmed to generate accurate time delays and periodic waveforms.

Features and Capabilities

The 8253 timer offers the following features and capabilities:

• Three independent 16-bit counters
• Programmable operating modes
• High accuracy and resolution
• Interrupt generation

Modes of Operation

The 8253 timer supports three modes of operation:

1. Mode 0: Interrupt on Terminal Count

In this mode, the counter generates an interrupt signal when it reaches its terminal count. It is commonly used for generating accurate time delays and periodic interrupts.

1. Mode 1: Programmable One-Shot

Mode 1 is used for generating a single pulse of a specified duration. It is often used in applications where a precise timing signal is required.

1. Mode 2: Rate Generator

In this mode, the counter generates a square wave with a programmable frequency. It is commonly used for generating clock signals and timebase references.

Programming the 8253 Timer

To program the 8253 timer, the microprocessor sends specific control words to the device. These control words determine the operating mode, counting method, and other parameters of the timer. By configuring the control words, the microprocessor can achieve the desired timing requirements.

8254 Programmable Interval Timer

The 8254 programmable interval timer is another commonly used peripheral device in microprocessor systems. It provides similar timing and counting capabilities as the 8253 timer but with additional features.

Overview and Functions

The 8254 timer consists of three counters: Counter 0, Counter 1, and Counter 2. Each counter can operate independently and perform different timing functions.

Counter 0 is typically used as a system timer and generates periodic interrupts at a fixed frequency. Counter 1 and Counter 2 can be programmed for various timing operations such as pulse generation, frequency measurement, and event counting.

Programming the 8254 Timer

To program the 8254 timer, the microprocessor sends control words to the device's control register. These control words specify the operating mode, counting method, and other parameters for each counter. By configuring the control words, the microprocessor can utilize the desired timing functions of the 8254 timer.

Real-World Applications

The 8254 timer finds applications in various real-world scenarios, including:

• Real-time operating systems
• Multimedia systems
• Industrial automation
• Robotics

8259A Programmable Interrupt Controller

The 8259A programmable interrupt controller is a vital peripheral device that manages interrupts in microprocessor systems. It allows the microprocessor to handle multiple interrupt sources and prioritize them based on their importance.

Introduction and Purpose

The 8259A interrupt controller serves the following purposes:

• Accepting interrupt requests from various devices
• Prioritizing interrupts
• Masking interrupts
• Generating interrupt vectors

Interrupt Handling Process

When an interrupt request is received, the 8259A interrupt controller performs the following steps:

1. Identifies the interrupt source
2. Determines the priority of the interrupt
3. Masks or enables the interrupt based on its priority
4. Sends an interrupt vector to the microprocessor

Programming the 8259A Interrupt Controller

To program the 8259A interrupt controller, the microprocessor sends specific control words to the device's control registers. These control words configure the interrupt masks, interrupt priorities, and other parameters of the interrupt controller.

Real-World Examples

The 8259A interrupt controller is widely used in various applications, including:

• Personal computers
• Embedded systems
• Communication systems
• Control systems

8257 DMA Controller

The 8257 DMA (Direct Memory Access) controller is a programmable peripheral device that enhances data transfer capabilities in microprocessor systems. It allows data to be transferred between memory and I/O devices without involving the microprocessor.

Overview and Role

The 8257 DMA controller performs the following functions:

• Transfers data between memory and I/O devices
• Manages data transfer modes
• Provides data transfer control signals

DMA Transfer Modes

The 8257 DMA controller supports three transfer modes:

1. Single Transfer Mode

In this mode, the DMA controller transfers a single block of data between memory and an I/O device. It is suitable for small data transfers.

1. Block Transfer Mode

Block transfer mode allows the DMA controller to transfer multiple blocks of data between memory and an I/O device. It is commonly used for large data transfers.

1. Demand Transfer Mode

Demand transfer mode enables the DMA controller to transfer data between memory and an I/O device on-demand. It is useful for real-time data streaming applications.

Programming the 8257 DMA Controller

To program the 8257 DMA controller, the microprocessor sends control words to the device's control registers. These control words specify the transfer mode, memory addresses, and other parameters for data transfer. By configuring the control words, the microprocessor can initiate and manage efficient data transfers using the DMA controller.

Real-World Examples

The 8257 DMA controller is widely used in applications that require high-speed data transfer, such as:

• Disk controllers
• Graphics cards
• Network adapters
• Audio and video processing

USART

USART (Universal Synchronous/Asynchronous Receiver/Transmitter) is a programmable peripheral device that enables serial communication between microprocessors and external devices.

Introduction

USART supports both synchronous and asynchronous communication modes and provides various features for reliable data transmission.

USART Communication Modes

1. Synchronous Mode

In synchronous mode, the USART uses a clock signal to synchronize the data transmission between the microprocessor and the external device. It ensures accurate and reliable data transfer but requires a dedicated clock line.

1. Asynchronous Mode

In asynchronous mode, the USART does not rely on a clock signal for data synchronization. Instead, it uses start and stop bits to mark the beginning and end of each data frame. Asynchronous mode is more flexible and widely used in serial communication.

Programming USART

To program the USART, the microprocessor configures its control registers with specific settings such as baud rate, data format, and communication mode. By setting these registers, the microprocessor can establish and control serial communication with external devices.

Real-World Applications

USART is extensively used in various applications, including:

• Serial communication interfaces
• Modems
• GPS receivers
• Wireless communication systems

Serial I/O

Serial I/O refers to the process of transmitting and receiving data one bit at a time. It offers several advantages over parallel I/O, including reduced pin count, simplified circuitry, and longer transmission distances.

Overview

Serial I/O involves the use of serial communication protocols such as RS-232, SPI (Serial Peripheral Interface), and I2C (Inter-Integrated Circuit). These protocols define the electrical and data transfer characteristics for serial communication.

Serial Communication Protocols

1. RS-232

RS-232 is a widely used serial communication protocol that defines the voltage levels, signal timing, and data format for serial communication between devices. It is commonly used for connecting computers to peripheral devices.

1. SPI

SPI is a synchronous serial communication protocol that allows multiple devices to be connected in a master-slave configuration. It provides high-speed data transfer and is commonly used in embedded systems and integrated circuits.

1. I2C

I2C is a multi-master serial communication protocol that enables communication between multiple devices using a two-wire interface. It is widely used in applications that require low-speed data transfer and control.

Programming Serial I/O

To program serial I/O, the microprocessor configures the control registers of the serial interface with specific settings such as baud rate, data format, and communication protocol. By setting these registers, the microprocessor can transmit and receive data using the serial interface.

Real-World Examples

Serial I/O is used in various applications, including:

• UART (Universal Asynchronous Receiver/Transmitter) interfaces
• Sensor modules
• Display modules
• Data loggers

Data Communication

Data communication is a fundamental aspect of microprocessor systems that involves the transmission and reception of data between devices. It enables devices to exchange information and perform coordinated actions.

Importance of Data Communication

Data communication is essential for the following reasons:

• Sharing data between devices
• Coordinating actions between devices
• Enabling remote control and monitoring
• Facilitating networking and internet connectivity

Data Communication Protocols and Standards

Data communication relies on various protocols and standards to ensure reliable and efficient data transfer. Some commonly used protocols include:

• Ethernet
• Wi-Fi
• Bluetooth
• USB

Data Transmission Methods

Data transmission can be classified into two methods:

1. Synchronous Transmission

In synchronous transmission, data is transmitted in a continuous stream using a clock signal for synchronization. It ensures accurate and reliable data transfer but requires a dedicated clock line.

1. Asynchronous Transmission

In asynchronous transmission, data is transmitted in individual frames with start and stop bits to mark the beginning and end of each frame. Asynchronous transmission is more flexible and widely used in serial communication.

Real-World Applications

Data communication is integral to various applications, including:

• Local area networks (LANs)
• Wide area networks (WANs)
• Internet of Things (IoT) systems
• Telecommunication systems

Advantages and Disadvantages of Programmable Peripheral Devices

Programmable peripheral devices offer several advantages in microprocessor systems:

• Flexibility: These devices can be programmed to perform specific functions based on the application requirements.
• Efficiency: Programmable devices offload tasks from the microprocessor, allowing it to focus on other critical operations.
• Cost-effectiveness: Using programmable devices eliminates the need for dedicated hardware components, reducing overall system costs.

However, there are also some disadvantages and limitations to consider:

• Complexity: Programming and configuring these devices may require specialized knowledge and skills.
• Compatibility: Compatibility issues may arise when integrating programmable devices from different manufacturers.
• Limited Functionality: Programmable devices may have limitations in terms of performance, features, and compatibility with other system components.

When selecting programmable peripheral devices for specific applications, it is essential to consider factors such as functionality, compatibility, performance, and cost.

Conclusion

Programmable peripheral devices play a vital role in microprocessor systems by enabling data communication and I/O operations. The 8253 and 8254 timers provide accurate timing and counting capabilities, while the 8259A interrupt controller manages interrupts and prioritizes them. The 8257 DMA controller enhances data transfer efficiency, and USART and serial I/O enable serial communication. Data communication is crucial for sharing information and coordinating actions between devices. Programmable peripheral devices offer advantages such as flexibility, efficiency, and cost-effectiveness, but they also have limitations. By understanding the features, programming techniques, and real-world applications of these devices, engineers can design and implement efficient microprocessor systems.

Summary

Programmable peripheral devices are essential in microprocessor systems for data communication and I/O operations. The 8253 and 8254 timers provide accurate timing and counting capabilities, while the 8259A interrupt controller manages interrupts and prioritizes them. The 8257 DMA controller enhances data transfer efficiency, and USART and serial I/O enable serial communication. Data communication is crucial for sharing information and coordinating actions between devices. Programmable peripheral devices offer advantages such as flexibility, efficiency, and cost-effectiveness, but they also have limitations. By understanding the features, programming techniques, and real-world applications of these devices, engineers can design and implement efficient microprocessor systems.

Analogy

Imagine a group of musicians performing in a concert. The programmable peripheral devices can be compared to the different instruments they play. Each instrument has its unique features and capabilities, just like the programmable devices. The musicians can program their instruments to play specific notes and rhythms, similar to how the microprocessor programs the peripheral devices. Together, the musicians and their instruments create a harmonious performance, representing the efficient functioning of a microprocessor system with programmable peripheral devices.