Internal RAM Structure of 8051 | Bit Addressable Area & General Purpose Area of Internal RAM in 8051

Summary

This video lecture delves into the internal RAM structure of the 8051 microcontroller, detailing its 128-byte capacity divided into three regions: the register bank area, bit-addressable RAM, and general-purpose RAM. It explains how to select register banks using PSW bits and execute instructions specific to the chosen bank. The video also covers bit-addressable operations and the utilization of the general-purpose area for stack operations and subroutines, offering insights into the microcontroller's memory management.

Takeaways

• 📘 The 8051 microcontroller has an internal RAM of 128 bytes, divided into three distinct regions: Register Bank, Bit Addressable RAM, and General Purpose RAM.
• 🔢 The Register Bank consists of 32 bytes, with four banks (Bank 0 to Bank 3), each containing eight registers (R0 to R7), and is selected using the PSW (Program Status Word) RS bits.
• 📍 The addresses for the Register Banks are Bank 0: 00h to 07h, Bank 1: 08h to 0Fh, Bank 2: 10h to 17h, and Bank 2: 18h to 1Fh.
• 🎯 The Bit Addressable RAM area spans 16 bytes from 20h to 2Fh, allowing for operations to be performed on individual bits within these bytes.
• 🤖 The 128 bits in the Bit Addressable area can be addressed individually, offering both byte-wise and bit-wise operations.
• 🔧 The General Purpose RAM area, also known as Scratchpad RAM, comprises 80 bytes from 30h to 7Fh and is used for various purposes as determined by the programmer.
• 🛠️ Instructions like 'MOV A, R0' depend on the selected Register Bank, which can be identified by the RS bits in the PSW register.
• 📝 Direct addressing can be used for certain operations, such as 'MOV A, #08h', which copies data from a specific address in RAM to the accumulator.
• 🔄 The stack pointer holds the address of the top of the stack within the internal RAM and is used for 'PUSH' and 'POP' operations.
• 🔑 The default Register Bank is Bank 0, but programmers can select other banks using the PSW RS bits, affecting which R0 to R7 registers are accessed.
• 📚 Understanding the internal RAM structure of the 8051 microcontroller is crucial for effective programming and utilizing its features.

Q & A

What is the total size of the internal RAM in a microcontroller 8051?

The total size of the internal RAM in a microcontroller 8051 is 128 bytes.

How is the internal RAM of the 8051 microcontroller divided?

The internal RAM of the 8051 microcontroller is divided into three regions: the register bank region, the bit-addressable RAM area, and the general-purpose RAM area.

How many register banks are there in the 8051 microcontroller, and what are their sizes?

There are four register banks in the 8051 microcontroller, each containing eight registers (R0 to R7), totaling 32 bytes.

What is the purpose of the PSW 0.3 and PSW 0.4 bits in the 8051 microcontroller?

The PSW 0.3 and PSW 0.4 bits are used to select the register bank in the 8051 microcontroller. By setting these bits, the programmer can choose between Bank 0, Bank 1, Bank 2, or Bank 3.

How can you determine which register bank is currently selected when executing instructions?

The currently selected register bank can be determined by the state of the RS bits (PSW 0.3 and PSW 0.4). The default bank is Bank 0, but it can be changed by setting these bits accordingly.

What is the address range of the bit-addressable RAM area in the 8051 microcontroller?

The bit-addressable RAM area in the 8051 microcontroller starts from address 20h and goes up to 2Fh, totaling 16 bytes.

How many bits are there in the bit-addressable RAM area of the 8051 microcontroller?

There are 128 bits in the bit-addressable RAM area of the 8051 microcontroller, as it consists of 16 bytes, and each byte has 8 bits.

Can you perform both bytewise and bitwise operations on the bit-addressable RAM area?

Yes, you can perform both bytewise and bitwise operations on the bit-addressable RAM area, although the area is specifically designed for bitwise addressing.

What is the purpose of the general-purpose RAM area in the 8051 microcontroller?

The general-purpose RAM area, also known as scratchpad RAM, is used for temporary storage of data and can be utilized by the programmer for various purposes, such as stack operations, subroutine calls, and ISRs.

What is the address range of the general-purpose RAM area in the 8051 microcontroller?

The general-purpose RAM area in the 8051 microcontroller ranges from address 30h to 7Fh, totaling 80 bytes.

What is the role of the stack pointer in the internal RAM of the 8051 microcontroller?

The stack pointer holds the address of the top of the stack within the internal RAM of the 8051 microcontroller and is used for push and pop operations.

Outlines

00:00

📚 Introduction to 8051 Microcontroller's Internal RAM Structure

This paragraph introduces the topic of the 8051 microcontroller's internal RAM structure. It explains that the internal RAM is 128 bytes in size, with addresses ranging from 00h to 7Fh. The RAM is divided into three regions: the Register Bank area, the bit-addressable RAM area, and the general-purpose RAM area. The paragraph also mentions the concept of selecting a Register Bank using the PSW (Program Status Word) bits RS0 and RS1, and provides an example of how to change the active Register Bank using assembly instructions.

05:01

🔍 Detailed Explanation of Bit-Addressable and General-Purpose RAM in 8051

The second paragraph delves deeper into the bit-addressable RAM area, which consists of 16 bytes that can be addressed individually as 128 bits, with addresses ranging from 20h to 2Fh. It explains how to perform bit-wise operations on these locations, such as setting or clearing specific bits. The paragraph also discusses the general-purpose RAM area, which is a larger section of 80 bytes (from 30h to 7Fh) that can be used flexibly by the programmer for various purposes, including stack operations, subroutine calls, and ISR (Interrupt Service Routines). The importance of understanding the stack pointer, which holds the address of the top of the stack within the RAM, is highlighted, with a promise to cover this topic in a future video.

Keywords

💡Microcontroller 8051

The Microcontroller 8051 is a specific type of microcontroller, which is a small computer on a single integrated circuit. It is known for its simplicity and efficiency, making it a popular choice for various embedded systems. In the video, the internal RAM structure of this microcontroller is the main focus, highlighting its significance in understanding how the device operates and stores data.

💡Internal RAM

Internal RAM, or Random Access Memory, refers to the memory inside a microcontroller where data can be read from and written to directly. In the context of the 8051 microcontroller, the script explains that it has 128 bytes of internal RAM, which is divided into different regions for specific purposes, such as register banks, bit-addressable RAM, and general-purpose RAM.

💡Register Bank

A Register Bank in the context of the 8051 microcontroller is a collection of registers that are used to store data temporarily. The script mentions that there are four register banks (Bank 0 to Bank 3), each containing eight registers (R0 to R7). These banks are crucial for data manipulation and are selected using the PSW (Program Status Word) bits.

💡PSW (Program Status Word)

PSW is a special register in the 8051 microcontroller that contains status flags and control bits. The script explains that two bits of the PSW, specifically bits 0.3 and 0.4, are used to select the active register bank, which determines which set of registers (R0 to R7) the programmer is currently working with.

💡Bit-addressable RAM

Bit-addressable RAM is a section of memory where each bit can be accessed individually. The script specifies that the 8051 microcontroller has 16 bytes of bit-addressable RAM, ranging from addresses 20H to 2FH. This feature allows for more granular control over data, enabling operations on individual bits rather than entire bytes.

💡General Purpose RAM

General Purpose RAM, also known as scratchpad RAM, is a section of memory that can be used for any purpose the programmer defines. The script mentions that the 8051 microcontroller has 80 bytes of general-purpose RAM, which can be utilized for various tasks such as storing temporary data or managing subroutines and interrupts.

💡Stack Pointer

The Stack Pointer is a register in the 8051 microcontroller that holds the address of the top item on the stack. The stack is a region of memory used to store temporary data during function calls or interrupt handling. The script indicates that the stack pointer will be discussed in more detail in a future video, emphasizing its importance in managing the microcontroller's memory operations.

💡Instruction Execution

Instruction execution refers to the process by which a microcontroller carries out the operations specified by its program instructions. The script gives examples of how instructions interact with the internal RAM, such as copying data from a specific register (e.g., 'MOV A, R0') or directly addressing a memory location (e.g., 'MOV A, #08H').

💡Bitwise Operations

Bitwise operations are operations that act on the individual bits of a byte or word. The script explains that in the bit-addressable RAM area, instructions like 'SETB 7FH' set a specific bit, while 'CLR 08H' clears a bit. These operations allow for precise manipulation of data at the bit level.

💡Memory Addressing

Memory addressing refers to the method by which a microcontroller accesses specific locations in memory. The script discusses different addressing modes, such as direct addressing (e.g., 'MOV A, 17H') and indirect addressing through the use of registers, which is essential for understanding how data is retrieved and stored within the microcontroller's RAM.

Highlights

Introduction to the internal RAM structure of the microcontroller 8051.

The size of internal RAM in the 8051 microcontroller is 128 bytes.

Internal RAM is divided into three regions: Register Bank, bit-addressable RAM, and general-purpose RAM.

There are four Register Banks (Bank 0 to Bank 3), each with eight registers.

Register Banks occupy 32 bytes with addresses ranging from 00h to 1Fh.

Bank selection is controlled by PSW 0.3 and PSW 0.4 bits.

Instructions execution depends on the selected Register Bank.

Direct address writing is possible for accessing specific registers.

16 bytes of bit-addressable RAM start from address 20h to 2Fh.

128 bits are available for bit-addressable operations.

Bit-addressable RAM allows both bytewise and bitwise operations.

General-purpose RAM area spans from 30h to 7Fh, totaling 80 bytes.

The programmer must decide how to utilize the general-purpose RAM area.

The stack pointer holds the address of the top of the stack within the internal RAM.

Future videos will explain the stack pointer's role in push and pop operations.

The video aims to provide a clear understanding of the 8051 microcontroller's internal RAM structure.

Transcripts

welcome to engineering Funda family this

video is a part of microcontroller 8051

video lecture series and in this video

I'll be going to explain you internal

Ram structure of microcontroller 8051

here there are few basic things that you

should know regarding how internal

structure is there with ram first of all

let me tell you what is the size of

internal Ram with microcontroller 8051

see that size is of 128 byte so

obviously address will start from 0 0

hex it will go up to 7 F hex 0 0 means 0

7 f means 127 so 0 to 127 means in total

128 bytes are there with internal Ram of

8051 those 128 bytes are bisected into

three regions first is resistor Bank

region second is based on bit

addressable Ram area and third is there

for general purpose scratch paid Ram

how it is there let us see all those

things step by step along with examples

so here let me explain you first how

resistor Bank area is there with Ram

with 8051 so here we have in total four

resistor banks that you should know Bank

0 Bank 1 Bank 2 Bank 3. each resistor

bank is having eight resistors r0 to R7

you see it is written over here

Bank 0 is having address from 0 0 hex to

zero seven hex Bank 1 is having address

from 0 8 to 0 f bank 2 is having address

from 1 0 to 1 7 and Bank 3 is having

address from one eight to one F in total

32 bytes are there But Here My Dear

students when you write program at that

time first of all you will have to

select the bank by default it will be

having Bank zero but as if programmer

wants to use any other bank then by

using two bits PSW 0.3 PSW 0.4 those are

rs bit of lag resistor by using this two

bit we can select any resistor Bank

here for example as if I write CLR PSW

0.4 what I do is I am clearing this bit

means this bit is zero when I write satb

PSW 0.3 means I am setting this bit PSW

0.3 what it means RS is 0 1 now RSA 0 1

means what now I have selected bank one

so now bank once resistors that is

getting selected as per r0 to R7 right

now my dear students when you execute

instructions at that time also there are

few interesting things that you need to

note down for example when you write

move a comma r0 what you do simply you

are copying the data of r0 inside a but

do you know which r0 that you are having

for that you need to know what is my RS

bits by default obviously it will be 0 0

for Bank 0 right by default it will be

taking this address 0 0 means r0's data

inside this resistor Bank but as if you

have this PSW 0.3 and PSW 0.4 as per

other bits means as if I say RS is

equals to 1 0 means bank 2 will be

selected and Bank 2's are 0 is having

address 1 0 hex Bank zeros are 0 is

having address 0 0 hex that is how it is

there right so here you can execute this

instruction there is no doubt based on

that but here you should know

which bank that we have selected

initially by default obviously it will

be Bank zero but you can change that

also right now here one more thing that

you need to know like you can execute Mo

a comma 0 8 hex now it is not like you

are copying 0 8 inside a my dear

students to copy 0 8 hex inside a you'll

have to write hashtag over here here I

have not written hashtag what it means

this is address which address Ram's

address so you see 0 8 hacks that is a

Rams address which is holding r0 inside

Bank 1 that is having whatever data that

I can copy inside a

so directly address also can be written

it is not like you will have to select

resistor Bank like for example is a as

if I write 1 7 hex over here then 1 7

hacks

that is R7 of bank 2. so that data which

is there with R7 of bank 2 that we will

be copying inside a as if you write this

instruction right so directly address

can be written over here

now my dear students let me explain you

second area of internal Ram that is bit

addressable area

here you see we have 16 bytes which are

bit addressable over here it is starting

from 2 0 hex to 2 F hex right in total

16 bytes are there which can be

addressed as per bit

Here My Dear students how many bits are

there with this 16 bytes obviously 16

into 8 means 128 bits are there

how to address this so obviously it will

start from 0 0 it will come over here up

to 0 7 means 20 hex that is having 0 to

0 7 bit address then 21 hex that is

having address from 0 8 to 0 f that is

how

up to 2fx that is having 7 f 2 7 8 hex

bit addressable that is how it is there

so here you can address that as per bit

as well as byte but spatially bit

addressable that I have mentioned the

reason is this

memory locations that can be addressed

as per bits all these memory locations

cannot be addressed as per bits right

bytewise operation can be done but

bitwise is also possible

let me explain you few examples like

when you execute set B 7 F hex what you

do see 7f hex means MSB of 2f hex that

is this bit MSB only right single bit so

this bit that will get set over here

when you execute this for example let me

execute

clr08 hex what you do you will be

clearing this bit which is having

position 0 at hex 0 at X is over here

that is LSB of 2 1 hex so that bit will

get clear so single bit clear that can

be done over here for example when you

write Mo to 0 hex comma hashtag FFX then

what do you do Here My Dear students at

2 0 hacks

you will be copying this data this data

is what all ones so eight ones are there

all eight ones that will be copying at

the address to 0 hex so 2 0 hex is

having this bits all bits will become 1

after this so bytewise operation is also

possible but bitwise is also possible

this is basically used for bit

addressable area right all the resistors

as well as all the locations that can be

performed with respect to byte but bit

wise spatially this addresses are only

available right so this 16 bytes in

total 128 bits that can be used as a bit

addressable with the internal Ram

structure of 8051 microcontroller now

third

category that is general purpose area in

Ram that is also referred as scratch

bedroom you see three zero hex to 7fx in

total 80 bytes are there that we can use

it for general purpose Here My Dear

students first of all programmer will

have to

to decide how to use this it is not like

automatically things will happen right

here programmer will have to program

things in such a way so that programmer

can use this general purpose area right

so here by using push and pop

instruction you can use this as well as

in call subroutine as well as in ISR

this area can be utilized right so here

in total 128 bytes are there 32 bytes

are there for resistor Bank 16 bytes are

there for bit addressable RAM and 80

bytes are therefore general purpose

right and this is how internal rhyme

structure is there and one more

essential thing that you need to know

down like stack pointer that will be

holding address of top of Stack that is

that inside this Ram only right and that

is used for push and pop so that is also

I'll explain you in future coming video

so that you will be having fair enough

idea about this I hope it is clear to

you still if any confusion is just post

that in the next I'll be happy to help

you thank you so much for watching this

video