Important parts of 8051 Microcontroller | Accumulator of 8051 | Program Counter of 8051 | 8051

Summary

This video lecture delves into the intricacies of the 8051 microcontroller, focusing on key components like the 8-bit ALU that handles arithmetic and logical operations, including single-bit manipulation. It explains the role of the accumulator A, register B for multiplication and division, and the program counter (PC) in instruction execution. The video also covers the data pointer (DPTR) for addressing data in RAM or external memory, the stack pointer (SP) for managing the stack memory, and the program status word (PSW) that reflects the status of the program after each instruction. Examples and further explanations are promised in upcoming videos to clarify these concepts.

Takeaways

• 😀 The 8051 microcontroller's ALU (Arithmetic and Logic Unit) is an 8-bit unit responsible for executing instructions and performing arithmetic and logical operations.
• 🔢 The ALU in the 8051 can perform both 8-bit and single-bit operations, such as adding the accumulator to a register or complementing a specific bit of a port.
• 📦 The accumulator (A) is an 8-bit register that is central to most arithmetic and logical operations in the 8051, often used as the primary operand for these operations.
• 📈 Register B, also 8-bit, is specifically dedicated to multiplication and division instructions in the 8051, storing results in a combined form with the accumulator for 16-bit results.
• 🔄 The program counter (PC) is a 16-bit register that points to the address of the next instruction to be executed in the program memory (ROM).
• 📌 The data pointer (DPTR) is a 16-bit register used to point to data in the data memory (RAM) or external memory, and can also be used for lookup tables in ROM.
• 🔠 The stack pointer (SP) is an 8-bit register that holds the address of the top of the stack in the internal RAM, used for last-in, first-out operations.
• 🔄 The stack memory is used for storing return addresses for subroutines and interrupt service routines, and is pointed to by the stack pointer.
• 📈 The program status word (PSW) is an 8-bit register that reflects the status of the program, such as carry and overflow flags, and can be altered by specific instructions.
• 🔑 The PSW register is bit-addressable, allowing for individual bit manipulation to set or clear specific flags, influencing program control flow.
• 🛠️ The 8051 microcontroller is based on the Harvard architecture, with separate memory spaces for program (ROM) and data (RAM), each pointed to by the PC and DPTR respectively.

Q & A

What is the primary function of the ALU in the 8051 microcontroller?

The ALU (Arithmetic and Logic Unit) in the 8051 microcontroller is responsible for executing instructions along with performing arithmetic and logical operations. It is an 8-bit unit that can also perform single-bit operations.

What is the significance of the accumulator in the 8051 microcontroller?

The accumulator, labeled as 'A', is an 8-bit register that is used for most arithmetic and logical operations in the 8051 microcontroller. It is central to the microcontroller's operations as many instructions are executed with respect to the accumulator.

What is the purpose of register B in the 8051 microcontroller?

Register B in the 8051 microcontroller is an 8-bit register dedicated to multiplication and division instructions. It works in conjunction with the accumulator to store the results of these operations, with B holding the higher byte and A holding the lower byte.

How does the 8051 microcontroller handle multiplication and division results?

When performing multiplication or division, the 8051 microcontroller stores the result in the accumulator (A) and register B. For multiplication, the 16-bit result is stored with B holding the higher byte and A the lower byte. For division, the quotient is in A and the remainder in B.

What is the role of the program counter (PC) in the 8051 microcontroller?

The program counter (PC) in the 8051 microcontroller is a 16-bit register that holds the address of the next instruction to be executed. It automatically increments after fetching an instruction, pointing to the subsequent instruction in the program memory.

How is the data pointer (DPTR) used in the 8051 microcontroller?

The data pointer (DPTR) in the 8051 microcontroller is a 16-bit register that holds the address of data in the data memory, which is RAM. It can also point to external RAM and is used for indexing and accessing lookup tables in ROM.

What is the purpose of the stack pointer (SP) in the 8051 microcontroller?

The stack pointer (SP) in the 8051 microcontroller is an 8-bit register that holds the address of the top of the stack in the internal RAM. It is used for managing the stack, which operates on a last-in, first-out basis and is crucial for subroutine and interrupt handling.

What is the role of the Program Status Word (PSW) in the 8051 microcontroller?

The Program Status Word (PSW) in the 8051 microcontroller is an 8-bit register that indicates the status of the program, such as whether a carry or overflow has occurred. It changes after every instruction execution and can also be manually altered by specific instructions.

How does the 8051 microcontroller perform single-bit operations?

The 8051 microcontroller can perform single-bit operations through its ALU. For example, the instruction 'CPL P0.3' complements a single bit of port 0, demonstrating the ALU's capability to handle one-bit logical operations.

What is the initial address indicated by the stack pointer (SP) after a reset in the 8051 microcontroller?

After a reset, the stack pointer (SP) in the 8051 microcontroller indicates the address 07h of the internal RAM, which is part of the stack memory area.

How is the 8051 microcontroller's internal RAM structured in relation to the stack pointer (SP)?

The internal RAM of the 8051 microcontroller has a stack memory area that ranges from 00h to 7Fh in address. The stack pointer (SP), being an 8-bit register, points to this area and is used with push and pop instructions as well as in subroutine and interrupt operations.

Outlines

00:00

🤖 Introduction to 8051 Microcontroller Terminologies

This paragraph introduces the video lecture series on the 8051 microcontroller, focusing on key terminologies. The speaker plans to explain the functioning of the Arithmetic Logic Unit (ALU), the significance of the Accumulator (A), Register B, Program Counter (PC), Stack Pointer (SP), and Program Status Word (PSW). The ALU, an 8-bit unit, performs both arithmetic and logical operations, including single-bit operations. Examples are given to illustrate these concepts, such as adding values using the accumulator and complementing bits of a port.

05:02

📚 Understanding the 8051 Microcontroller's Memory Architecture

The second paragraph delves into the Harvard architecture of the 8051 microcontroller, which separates program and data memory. The internal ROM holds the program instructions, while the RAM stores data. The Program Counter (PC), a 16-bit register, points to the instruction addresses. As instructions are fetched and executed, PC automatically increments to the next instruction. The Data Pointer (DPTR), also 16 bits, points to data in RAM and can address external RAM or be used for lookup tables. The paragraph also explains the use of DPTR in index addressing with the 'movex' instruction.

10:03

🔄 Exploring the Stack Pointer and Program Status Word in 8051

This paragraph explains the function of the Stack Pointer (SP) in the 8051 microcontroller, which holds the address of the top of the stack in the internal RAM. The stack operates on a Last In, First Out (LIFO) principle and is used for subroutine and interrupt handling. The initial address of the SP after reset is 07h. Additionally, the Program Status Word (PSW) is discussed as an 8-bit register that reflects the status of the program, such as carry and overflow flags. The PSW changes after each instruction execution and can be manipulated with specific instructions. The speaker promises a future video detailing how the PSW works and its flags.

Keywords

💡Microcontroller

A microcontroller is a small computer on a single integrated circuit chip that contains a processor core, memory, and programmable input/output peripherals. In the context of the video, it is the main theme as the script discusses the 8051 microcontroller, highlighting its various components and functions.

💡ALU (Arithmetic Logic Unit)

The ALU is a part of the CPU that performs arithmetic and logical operations. In the video, it is explained that the 8051 microcontroller has an 8-bit ALU responsible for executing instructions and performing operations, which is central to understanding the microcontroller's computational capabilities.

💡Accumulator (A)

The accumulator is a register used in a processor for storing results of arithmetic and logic operations. The script emphasizes its significance in the 8051 microcontroller, where it is an 8-bit register involved in most arithmetic and logical operations, exemplified by the instruction 'add a, r1'.

💡Register B

Register B is an 8-bit register dedicated to multiplication and division operations in the 8051 microcontroller. The script illustrates its use in instructions like 'mul a, b', where the result of multiplying the accumulator and register B is stored, with B holding the higher byte.

💡Program Counter (PC)

The program counter is a register that stores the memory address of the next instruction to be executed. The script explains its 16-bit size in the 8051 and its role in pointing to the instruction address in the program memory, highlighting its automatic incrementation after each instruction fetch.

💡Data Pointer (DPTR)

The data pointer is a 16-bit register used to point to data in memory. The video script describes its function in accessing data memory in the 8051 microcontroller, with examples of how it can be used for external RAM addressing or as a pointer for lookup tables.

💡Stack Pointer (SP)

The stack pointer is an 8-bit register that holds the address of the top of the stack in memory. The script explains its role in managing the stack memory area within the internal RAM of the 8051, following the Last In, First Out (LIFO) principle, and its use in push and pop operations.

💡PSW (Program Status Word)

The PSW is an 8-bit register that reflects the status of the program, such as carry or overflow flags. The video script describes how it changes after each instruction execution and how it can be manipulated with specific instructions to set or clear flags, indicating the status of the program's operations.

💡Instruction Execution

Instruction execution refers to the process by which a microcontroller carries out the tasks defined by its program instructions. The script provides examples of how different instructions are executed by the 8051's ALU, affecting the state of registers like the accumulator and PSW.

💡Howard Architecture

The Howard architecture is a system design where program and data memories are separate. The script mentions that the 8051 microcontroller is based on this architecture, with internal ROM for program storage and RAM for data, which influences how the program counter and data pointer function.

Highlights

Introduction to the 8051 microcontroller and its key terminologies.

Explanation of the ALU's function within the 8051 microcontroller.

The 8-bit ALU's role in executing instructions and performing arithmetic and logical operations.

Capability of the ALU to perform single-bit operations in addition to 8-bit operations.

The significance of the Accumulator A in 8051 for most arithmetic and logical operations.

Description of the 8-bit Register B used for multiplication and division instructions.

How the multiplication instruction 'mul a b' stores a 16-bit result in A and B registers.

Division operation 'div a b' and how the quotient and remainder are stored in A and B registers.

Introduction to the Program Counter (PC) and its 16-bit size for instruction addressing.

Explanation of Harvard architecture in 8051 with separate memory for program and data.

The Data Pointer (DPTR), its 16-bit size, and its role in pointing to data in RAM or external memory.

Use of DPTR for accessing lookup tables in ROM through index addressing mode.

Introduction to the Stack Pointer (SP), its 8-bit size, and its function in managing the stack memory.

Stack memory's operation based on Last In, First Out (LIFO) principle and its relation to SP.

Explanation of the Program Status Word (PSW), its 8-bit size, and its role in indicating program status.

PSW's bit-addressability and the ability to change flag status through specific instructions.

Invitation for viewers to ask questions and get help in the comments section.

Transcripts

welcome to engineering fender family

this video is a part of microcontroller

eight zero five one video lecture series

and in this video i'll be going to

explain you few very interesting and

important terminologies of

microcontroller eight zero five one like

i'll explain you how alu is functioning

with eight zero five one

like what is the significance of

accumulator resistor b

as well as pc stack pointer and psw

resistor that is there with eight zero

five once i'll explain you each and

everything with example so that will

gives you more clarity let us see all

those things step by step so first of

all i'll explain you how alu is there so

arithmetic and logic unit that is a part

of cpu that you should know

here with 8051 we have 8 bits of alu

that is responsible for execution of

instruction along with arithmetic and

logical operation so all the arithmetic

and logical operation performed inside

cpu is been done by alu

size of alu is eight bits with eight

zero five one

here my dear students it is not only

eight bits of arithmetic and logical

operation that can be there with alu

here you can perform single bit

operation as well let me give you some

examples so that will give you more

clarity

for example when you execute

add a comma r1 all you do is you will be

adding accumulator a with r1

and the result will get stored inside a

you should know my dear students a

r0 to r7 all the resistor are having

size of 8 bits so here we have performed

8 bits of addition

when you execute cpl p

0.3 what you do is you will be

complementing this bit of port 0. port 0

is having 8 bits see here we have port

0. so this port 0 that is having 8 bits

in that

p 0.3 that is one bit of that port

that we can complement by this

instruction so this alu can perform one

bit operation as well so in short my

dear students you should know eight zero

five one performs eight bits of

arithmetic and logical operation as well

as it can perform one bit logical and

arithmetic operations

let me explain you

second term that is accumulator a

accumulator a that is a resistor with

size of 8 bits

here my dear students you should know

this is spatial resistor why the reason

is

most of the arithmetic and logical

operations of eight zero five one that

happens with respect to accumulator only

right

so here accumulator

is used with most of the arithmetic and

logical operations

here if i give you some example then it

will gives you more clarity like when

you write add a comma r0 what you do you

will be adding a with r0 and answer will

get stored inside a

as if you execute a and l

what you do is you perform logic and

operation

when you write a n l then a comma r 1

then you will be performing logic and

operation of a with r 1 and then you

will be storing answer inside a

so almost all the arithmetic and logical

operation that can be executed along

with

resistor which is accumulator a

now my dear students i'll explain you

one more essential resistor which is

resistor b it is also having size of 8

bits and this is dedicatedly provided

with 8051

for multiplication and division

instructions

let me give you example

like when you write mul a b what you do

you multiply a and b and then

answer will get stored inside ba

you see when you have two data

multiplication that data is having size

of 8 bits only accumulator is having

size of 8 bit

this b is having size of 8 bit when you

multiply 8 bit into 8 bit your answer

will be of 16 bits

so 16 bits that will get stored inside

again

ba where b will hold higher byte and a

will hold lower byte that is how it is

getting stored inside ba so b is

dedicatedly provided for multiplication

and division when you write div a b what

you do you will be doing

a divided by b operation

now

here when you perform this your answer

will be there in terms of quotient and

reminder

so quotient will be there inside a after

a divided by b and remainder will be

there inside b after a divided by b that

is how a and b

resistors are there inside 8 0 5 1.

now my dear students i'll explain you

how program counter is there

so you should know my dear students

8051

that is based on howard architecture

howard architecture means what

howard architecture means

for program and for data we will be

having separate memory

you see here internally we have 4 kb of

rom and 128 byte of ram

so ram will be holding data and rom will

be holding program means instructions so

address

of instruction inside program will be

pointed by pc

so whenever you execute any program

you will be executing that with respect

to one by one instructions

so that instruction address that will be

pointed by pc it is having size of 16

bits

and

you will be observing instruction

address that will be there with pc so

when you fetch one

automatically pc will get increment and

it will be pointing next instruction to

be executed so for example here you are

writing program

let us say first instruction that is

getting fetch pc will get automatically

incremented by one it will be now

pointing next instruction once first

instruction is getting executed

pc is already having next instructions

address so now next instruction is ready

to be fetched

once next instruction is getting fetch

pc again will get automatically get

incremented and it will be pointing

third instruction and it will wait till

second instruction is getting executed

so what will happen is my dear students

pc

increments automatically once you

fetch any instruction and those

instructions will be there in program

memory means it will be there inside rom

only as eight zero five one is there

based on howard argue texture

now my dear students i'll explain you

dbdr data pointer data pointer dbdr that

is having size of 16 bits

right

and my dear students it will be holding

address of data in data memory data

memory will be ram always with 8051 it

is there with howard architecture

program memory will be rom data memory

will be ram

program memory will be pointed by pc

data memory will be pointed by dbdr that

is how it will be there you should know

that so here dptr

that is holding

data of ram memory

right so here you will be observing it

is further divided into two parts dbdr

means dph means higher byte of dvdr and

dpl means lower byte of dpdr here my

dear students this dptr that is of 16

bits what it means it is not pointing

internal ram you see internal ram is

having size of 128 bit so address of

internal ram

that is just

of 8 bits

but here how much

size is there with dpdr 16 bit so

obviously this dpdr that will be

pointing

external ram as if you interface

external ram then only

that data will be pointed by dpdr

remember this

it can also be used as a pointer for

lookup table

like you see what i have told you is

you will be using rom for which purpose

program program will be having what

instructions

and you will be using ram for which

purpose data right why we store data

inside ram the reason is data may be

volatile

but

in some cases

as if you wanted to have data

that should not be volatile in that case

what you will be doing

obviously if data is not volatile in

that case we must store inside rom when

you store those data

which are not volatile inside rom

at that time you will have to make

lookup table and you will have to store

it inside rom

and to access that

you can use this dptr so here what you

can do is you can make index addressing

mode by which we can have usage of dbdr

let me explain you by example

here when you have lookup table

operation at that time remember you will

have to write movex do not forget this x

right when you write x what you do is

you will be using dptr as per pointer

right

see normally what we write is move a

comma

any address right so at a time it will

be taking data inside a that is normal

move but when you use

this dpdr as a pointer for ram at a time

you will have to write x over here so

what will happen you see when you write

mu x a comma at the rate db dr means

ram is pointed by dbtr

and at that address whatever data is

there that you will be moving inside a

now you see i'll give you one example

which is the based on lookup table when

you want to access lookup table inside

rom at the time you'll have to use c

after move you'll have to write c when

you write move c a comma at the rate a

plus d b d r then all you do is

here a plus dptr that will be my address

that is the address of rom

and at that address whatever data is

there that i'll be moving inside

accumulator a that is how this move c is

operating so mosi is there in terms of

index addressing right

so that is how dpdr is working now my

dear students i'll be going to explain

you stack pointer

stack pointer is having size of 8 bits

and it will be holding address of top of

stack

you should know my dear students this

stack that is operating as per last in

first out

and address of that stack will be holded

by this eight bits of resistor which is

there with stack pointer and you should

know my dear students you see here we

have internal ram of eight zero five one

so this internal ram's address

that will be holded by stack pointer so

internal ram is having stack memory only

and address of that will be there with

sp you see 128 byte of internal ram is

there so 128 byte means what will be the

address range it will be starting from 0

0 hex and it will go up to 7 f hex so

that internal ram

will be

working with stack memory and that

memory will be pointed by stack pointer

resistor right so internal ram address

that is ranging from 0 0 hex to 7 f x

and that is having stack memory area

that is pointed by stack pointer

resistor we use that with push and pop

instructions as well as we use stack

memory in subroutine as well as

interrupt subroutine so this stack

memory which will be used for subroutine

as well as interrupt subroutine

when you reset this 8051 at that time

this tag pointer will indicate 0 7 hex

address of internal ram right

why the reason is this internal ram is

also holding resistors data right so on

reset it will be having initial address

of 0 7 with sp

here my dear students there are many

other things which is happening inside

this ram but here you just understand

this internal ram will be having stack

memory that will be pointed by stack

pointer that is having size of 8 bits it

will be having range from 0 0x to 7 fx

in future coming videos i'll explain you

how this internal ram structure is there

that will gives you more clarity

here my dear students when we talk about

psw then you should know it is program

status word

it is of 8 bits and it will be showing

you status like whether carry is there

or not like whether overflow is there or

not right so that is how status is

indicated by psw resistor and that

operation will be performed inside cpu

so whatever operation that we performed

by executing instruction after

every instruction execution this phw

flag will change

how it will change for that i'll make

separate video in that i'll show you how

all the flags are there here just

understand one thing psw is having size

of 8 bits it is holding status of

program and it will change after

every instruction execution

and we can also change the status of

flag by executing instructions like set

b psw 0.2 clear psw 0.2 so here we are

setting this bit we are clearing this

bit why the reason is psw is bit

addressable resistor so here bit by bit

operation can be performed as well as

you can have

complete

resistor

operations and this flag resistor is

showing you how program status is there

so in next coming videos i'll explain

you how psw is there so i think now

you are having fair enough idea about

how all these elements are there with

8051 still if any confusion is there

just post that in comments i'll be happy

to help you thank you so much for

watching this video