8051 Microcontroller:Features,Applications and Types

The 8051 microcontroller, developed by Intel in the 1980s, operates on the Harvard Architecture and was primarily engineered for Embedded Systems applications. Originally crafted using NMOS technology, Intel later revamped the 8051 Microcontroller using CMOS technology, resulting in a revised edition bearing the suffix 'C' in its name, such as the 80C51. These latest iterations of Microcontrollers consume less power compared to their predecessors. The 8051 Microcontroller finds extensive application across various domains, rendering projects involving it significant in engineering final year assessments. This article provides an overview of the architecture and operation of the 8051 microcontroller.

 

The Introduction of 8051 Microcontroller

 

The 8051 Microcontroller, introduced by Intel in 1981, is a type of integrated circuit featuring 40 pins encapsulated within a dual inline package (DIP). It encompasses 128 bytes of RAM, 4kb of ROM, and two 16-bit timers. Additionally, it offers four programmable 8-bit parallel ports, catering to various application needs. The architecture of the 8051 microcontroller relies on a system bus, facilitating the interconnection of all devices with the central processing unit. This bus comprises an 8-bit data bus, a 16-bit address bus, and bus control signals, enabling the interfacing of peripherals such as ports, memory, interrupt control, serial interface, CPU, and timers.

 

The 8051 Microcontroller features two distinct buses—one for program storage and another for data storage. Consequently, it provides separate storage spaces for programs and data, each capable of accommodating sizes of 64K by 8. Its core components include an 8-bit accumulator and an 8-bit processing unit, with the B register serving as a significant functional block. Programming for the 8051 microcontroller is typically executed using embedded C language through software like Keil. Additionally, it incorporates several other 8-bit and 16-bit registers to facilitate various operations.

 

Internally, the 8051 Microcontroller integrates built-in RAM for processing and operation. This primary memory serves to store temporary data but is volatile, meaning its contents are lost upon power shutdown. Known for its simplicity, cost-effectiveness, modest computing power requirements, straightforward architecture, and instruction set, the 8051 microcontroller remains a popular choice for numerous applications.

 

The Features of the 8051 Microcontroller

 

Key attributes of the 8051 microcontroller architecture include:

 

An 8-bit CPU comprising two registers, denoted as A and B.

8K Bytes of internal ROM, functioning as flash memory for programming capabilities.

Internal RAM totaling 256 Bytes, with the initial 128 Bytes divided into four banks, each containing eight registers. Additionally, there are addressable registers (16-bit) and general-purpose registers (80).

The remaining 128 bytes of RAM, from 80H to FFH, house Special Function Registers (SFRs), governing various peripherals such as serial ports, timers, and all I/O ports.

Support for interrupts, including two external and three internal interrupts.

Integrated oscillator and CLK circuitry.

Control registers such as PCON, SCON, TMOD, TCON, IE, and IP.

Two 16-bit timers or counters, referred to as T0 and T1.

A 16-bit program counter (PC) and a data pointer (DPTR).

32 I/O pins organized into four ports: P0, P1, P2, and P3.

An 8-bit stack pointer (SP) and a processor status word (PSW).

Serial data transmission (Tx) and reception (Rx) capabilities for full-duplex operation.

 

8051 Microcontroller Structure

 

The architecture of the 8051 microcontroller is depicted below. Let's delve into the components of the 8051 microcontroller design:

 

Central Processor Unit (CPU):

 

As you may know, the Central Processor Unit (CPU) serves as the brain of any processing device. It scrutinizes and orchestrates all operations conducted within the Microcontroller. Users have no direct control over the CPU's operations. It interprets the program stored in the ROM and executes the designated tasks. The CPU manages various registers within the 8051 microcontrollers.

 

Interrupts:

 

As implied by the heading, an Interrupt is a subroutine call that interrupts the primary function or task of the Microcontroller to execute another program of higher priority. Interrupts play a crucial role in handling urgent situations. They provide a means to temporarily halt the ongoing process, execute a sub-routine task, and then resume normal program execution.

 

The 8051 Microcontroller can be configured to temporarily pause or suspend the main program upon the occurrence of an interrupt. Once the sub-routine task is completed, the execution of the main program resumes automatically. The 8051 Microcontroller features five interrupt sources, including two peripheral interrupts, two timer interrupts, and one serial port interrupt.

 

8051 Microcontroller Design

 

The architecture of the 8051 microcontroller is illustrated below. Let's explore the characteristics of the 8051 microcontroller design:

 

 

Central Processor Unit (CPU):

 

As you may already know, the Central Processor Unit (CPU) serves as the core processing unit in any computing device. It analyzes and oversees all operations executed within the Microcontroller. Users do not directly control the CPU's operations. It interprets the program stored in the ROM and executes the designated tasks. The CPU manages various types of registers within the 8051 microcontrollers.

 

Interrupts:

 

As suggested by the heading, an Interrupt is a subroutine call that interrupts the primary function or task of the Microcontroller to execute another program of higher priority. Interrupts play a pivotal role in handling critical situations. They offer a mechanism to temporarily halt or postpone the ongoing process, execute a sub-routine task, and then resume normal program execution.

 

The 8051 Microcontroller can be configured to temporarily halt or suspend the main program upon the occurrence of an interrupt. Once the sub-routine task is completed, the execution of the main program resumes automatically. The 8051 Microcontroller features five interrupt sources, including two peripheral interrupts, two timer interrupts, and one serial port interrupt.

 

Memory:

 

The 8051 Microcontroller requires a program, which consists of a sequence of instructions. This program instructs the Microcontroller to execute specific tasks. To store and execute these programs, the Microcontroller requires a dedicated storage space, known as Program Memory or Code Memory. In simpler terms, this is often referred to as Read-Only Memory (ROM).

 

Additionally, the Microcontroller needs memory to temporarily store data or operands during its operations. This temporary data storage space is referred to as Data Memory, and Random Access Memory (RAM) is commonly used for this purpose. The 8051 Microcontroller features a 4KB ROM for program storage and 128 bytes of RAM for data storage.

 

Bus:

 

In essence, a bus is a group of wires that serve as a communication channel for data transfer. Buses typically consist of 8, 16, or more wires, allowing them to carry 8 or 16 bits of data simultaneously. There are two main types of buses:

 

Address Bus: The 8051 Microcontroller is equipped with a 16-bit address bus, used to address memory locations. It facilitates the transmission of addresses from the Central Processing Unit to memory.

 

Data Bus: The 8051 Microcontroller features an 8-bit data bus, which is used to transport data between various components within the Microcontroller.

 

Oscillator:

 

Given that the Microcontroller operates as a digital circuitry component, it necessitates a timer to regulate its functions. Hence, the 8051 Microcontroller is equipped with an on-chip oscillator, serving as a timing source for the Central Processing Unit (CPU). Due to the consistent output pulses of the oscillator, it enables synchronized operation of all components within the 8051 Microcontroller.

 

Input/Output Port:

 

Considering that the Microcontroller is utilized in embedded systems to oversee device functions, interfacing it with other equipment, devices, or peripherals necessitates Input/Output (I/O) ports. To fulfill this requirement, the 8051 Microcontroller features four I/O ports for connecting it to external peripherals.

 

Timers/Counters:

 

The 8051 Microcontroller is integrated with two 16-bit counters and timers. These counters are partitioned into 8-bit registers. The timers serve various functions, including interval measurement, pulse width determination, and more.

 

Types of Interrupts:

 

The 8051 microcontroller incorporates various types of interrupts, each sourced from different elements:

 

- TF0 (Timer 0 Overflow Interrupt)

- TF1 (Timer 1 Overflow Interrupt)

- INT0 (External Hardware Interrupt)

- INT1 (External Hardware Interrupt)

- RI/TI (Serial Communication Interrupt)

 

Memory:

 

In the architecture of the 8051 microcontroller, memory encompasses two main categories: program memory and data memory.

 

Program Memory houses the instructions executed by the CPU. Typically implemented as Read-Only Memory (ROM), the program stored within it persists even in the absence of power or during system resets.

 

Data Memory, on the other hand, is responsible for storing variables, temporary data, intermediate results, and other essential data required for the proper functioning of the program.

 

Timer and Control Unit:

 

The primary role of a timer is to create a time delay or interval between two events. Within the 8051 microcontroller, there are two timers, each operating as a 16-bit unit, allowing the system to generate two separate delays simultaneously, thereby facilitating the creation of the desired delay. Typically, microcontrollers utilize hardware timers, which are physical devices controlled by the processor to generate specific time delays.

 

These timers enable the microcontroller to produce delays as required by the processor and signal the processor once the designated delay has elapsed. By employing timers, the processor can execute other tasks while waiting for the delay to expire.

 

In addition to timers, the microcontroller features essential components such as a program counter, data pointer, stack, stack pointer, instruction registers with latches, temporary registers, and buffers for I/O ports. These elements collectively contribute to the microcontroller's functionality and enable it to execute various operations efficiently.

 

Registers:

 

Registers within microcontrollers serve as storage units for data and temporary instructions essential for processing addresses to retrieve data. The 8051 microcontroller is equipped with 8-bit registers, spanning from D0 to D7, where D0 to D7 represent the least significant bit (LSB) to the most significant bit (MSB), respectively.

 

To facilitate efficient data processing beyond 8 bits, data is often segmented into eight distinct bit parts. While the microcontroller features numerous registers, programmers primarily have access to general-purpose registers. These registers are typically categorized into two types: general-purpose and special-purpose. The following are some of the most common general-purpose registers:

 

- The accumulator, which executes arithmetic and logic instructions.

- Registers like B and R0 to R7 are utilized for storing instruction addresses and data.

- The Data Pointers register, or DPTR, enables and processes data in various addressing modes. Consisting of a high byte (DPH) and a low byte (DPL), this register holds a 16-bit address, serving as a base register for indirect jumps, lookup table instructions, and external data transfers.

- The Program Counter, or PC, is a 16-bit register that stores the address of the next instruction to be executed.

 

Except for the program counter and data pointer registers, these registers are all 8 bits in size.

 

Data Types:

 

In the realm of this microcontroller, a single 8-bit data type reigns supreme, with each register boasting an 8-bit size. Should data exceed 8 bits, it falls upon the programmer to segment the data into 8-bit components before undertaking processing tasks. Assemblers commonly utilize the DB directive in assembly language to manage data.

 

PSW Register:

 

The PSW, or Program Status Word, serves as a pivotal register within the microcontroller architecture. Also recognized as the flag register, it offers insights into the status of arithmetic logic instructions, including zero and carry bits. Constituting an 8-bit register, the PSW comprises 6 bits dedicated to conditional flags. These flags, known as conditional flags, dictate instruction execution based on specific conditions being met.

 

Among these conditional flags are overflow, parity, auxiliary carry, and carry. Furthermore, certain bits within the Program Status Word register, such as bits 3 and 4, facilitate bank register modifications, while bits 1 and 5 remain unused, yet can be repurposed by programmers to fulfill specific operational requirements.

 

Register Banks:

 

In the domain of stacks and register banks, a 32-byte RAM plays a pivotal role, meticulously partitioned into four distinct banks. Each bank houses eight registers, spanning from R0 to R7, where R0 and R7 delineate the RAM's initial and terminal locations, respectively. The second bank commences from location 8 and culminates at 05H. Subsequently, the third bank commences at 10H and concludes at location 17H. Finally, the fourth bank occupies the range from 18H to 1FH.

 

Stack:

 

A crucial segment of RAM, the stack serves as a temporary repository for data and addresses, vital for microprocessor operations. Given the inherent constraints on register availability for address and data storage within a microprocessor, the stack's significance cannot be overstated.

 

In the realm of 8051 microcontrollers, the stack is 8 bits wide, accommodating data spanning from 00 to FFH. The CPU utilizes the stack pointer to access the stack. Remarkably, this microcontroller features an 8-bit stack pointer, enabling it to accommodate values ranging from 00H to FFH. Upon activation, the stack pointer assumes an initial value of 07.

 

Organization of Memory:

 

The microcontroller boasts a sophisticated memory arrangement, featuring a distinct address bus designated for program memory, external RAM, and data memory. It adheres to the Harvard architecture, pioneered by Harvard in 1944.

 

Addressing Modes:

 

Microprocessors retrieve data through various means. Typically, data is accessed from memory, registers, or instant values. These diverse methods of data access are known as addressing modes. Different microcontrollers incorporate varying addressing modes, contingent upon manufacturers' designs. The addressing modes of this microcontroller encompass the following:

 

1. Register

2. Register Indirect

3. Immediate

4. Indexed

5. Direct

 

Applications of 8051 Microcontroller Architecture:

 

The applications of the microcontroller 8051 span a wide range of devices, primarily due to its ease of integration into projects or machine assemblies.

 

Energy Management: Efficient metering systems facilitate energy consumption calculations in residential and industrial settings. These meter systems are made efficient by incorporating microcontrollers.

Touchscreens: Many microcontroller suppliers incorporate touch sensing capabilities into their designs. Portable devices like media players, gaming consoles, and cell phones are examples of devices integrated with microcontrollers and touch sensing screens.

Automobiles: The 8051 microcontroller finds widespread use in providing automotive solutions. It is extensively employed in hybrid vehicles to control engine variations. Features such as cruise control and anti-lock braking systems have further enhanced its capabilities with the integration of microcontrollers.

Medical Devices: Portable medical devices such as glucose and blood pressure monitors utilize microcontrollers to display measurements, thereby providing higher reliability in delivering accurate medical results.

 

In summary

 

This covers an overview of the 8051 microcontroller architecture, its functioning, and its diverse applications. As a question for you: What are the different families available in the 8051 microcontrollers?