Addressing Modes of 8051 Microcontroller | Immediate | Register | Direct | Indirect | Indexed

Summary

This video from the microcontroller 8051 lecture series introduces and explains the five addressing modes of the 8051 microcontroller. It covers Immediate, Register, Direct, Indirect, and Indexed addressing modes with examples to clarify their applications in specifying operands for instructions. The explanation highlights the unique characteristics of each mode, such as using the accumulator for Register addressing and the use of the Data Pointer (DPTR) for Indirect addressing, as well as the distinction between accessing internal and external RAM and ROM through these modes.

Takeaways

• 📘 Addressing modes define how operands are specified in microcontroller 8051 instructions.
• 🔢 Immediate addressing mode involves specifying data directly in the instruction, prefixed with a hashtag (#).
• 💾 Register addressing mode uses registers like A and R0-R7 to specify operands and requires the accumulator for certain operations.
• 🏠 Direct addressing mode provides the address of the operand within the instruction, applicable for internal RAM or SFRs.
• 🔑 Indirect addressing mode uses a register to give the address of the operand, allowing access to internal and external RAM.
• 📍 External RAM access in 8051 requires 16-bit addressing with the DPTR register and the use of the 'X' in the 'MOVE' instruction.
• 🔄 Indexed addressing mode is used to access data from code memory, which is separate from data memory in the Harvard architecture.
• 🚫 Certain operations are not allowed, such as moving data directly between registers R0-R7 without using the accumulator in register addressing mode.
• 📡 SFRs have a specific address range from 80H to FFH, while internal RAM addresses range from 00H to 7FH.
• 🔣 Data in the instruction with a hashtag represents immediate data, which can be one or two bytes long.
• 🛠 The script provides examples to illustrate each addressing mode, emphasizing the differences and specific use cases.

Q & A

What are addressing modes in the context of microcontroller 8051?

Addressing modes in the context of microcontroller 8051 are ways of specifying operands in an instruction. They define how data or memory locations are referenced within the instruction set of the microcontroller.

How many addressing modes does the 8051 microcontroller have?

The 8051 microcontroller has five addressing modes.

What is Immediate Addressing Mode and how is data specified in it?

Immediate Addressing Mode is a way of specifying operands where the data is included in the instruction itself. Data is specified by writing a hashtag (#) before the data value, which can be one or two bytes.

What is the significance of the hashtag symbol in Immediate Addressing Mode?

In Immediate Addressing Mode, the hashtag symbol indicates that the following value is data that is to be used directly in the instruction, rather than a memory location or register.

Can you provide an example of Immediate Addressing Mode?

An example of Immediate Addressing Mode is 'MOV A, #15h', which moves the hexadecimal data 15h into register A.

What is Register Addressing Mode and which registers are used in it?

Register Addressing Mode is a way of specifying operands using registers. In the 8051 microcontroller, registers A and R0 to R7 are used for this purpose.

Why can't registers R0 to R7 be used directly with each other in Register Addressing Mode?

In the 8051 microcontroller, you cannot use registers R0 to R7 directly with each other in Register Addressing Mode because the accumulator must be used as an intermediary for data transfer between these registers.

What is Direct Addressing Mode and how is the operand's address specified?

Direct Addressing Mode is a way of specifying operands by providing the address of the operand directly in the instruction. This address can be for internal RAM or Special Function Registers (SFRs).

Can you give an example of Direct Addressing Mode?

An example of Direct Addressing Mode is 'MOV A, 35h', which moves the data from the internal RAM location 35h into the accumulator A.

What is Indirect Addressing Mode and how does it differ from Direct Addressing Mode?

Indirect Addressing Mode specifies the operand's address through a register. It differs from Direct Addressing Mode in that it uses a register to point to the address of the operand, rather than specifying the address directly in the instruction.

How is External RAM accessed in the 8051 microcontroller?

External RAM is accessed in the 8051 microcontroller using the Data Pointer (DPTR) register for 16-bit addressing or any of the registers R0 to R7 for 8-bit addressing with Indirect Addressing Mode.

What is Indexed Addressing Mode and what is its purpose?

Indexed Addressing Mode is used to access data from code memory. Its purpose is to access non-volatile data stored in ROM, such as ASCII data or data related to interfacing with a seven-segment display.

Can you explain how Indexed Addressing Mode works with an example?

Indexed Addressing Mode works by using an instruction like 'MOVC A, @A + DPTR', which means the data at the address calculated by adding the value in register A to the Data Pointer (DPTR) is moved into the accumulator A from the code memory.

Outlines

00:00

🤖 Introduction to Addressing Modes in Microcontroller 8051

This paragraph introduces the concept of addressing modes in the context of the 8051 microcontroller. Addressing modes are explained as methods for specifying operands in instructions. The 8051 microcontroller is highlighted to have five addressing modes, which will be detailed in the lecture. Immediate addressing mode is introduced first, where data is specified directly within the instruction using a hashtag (#). Examples are provided to illustrate how immediate data is used in instructions, and a note is made about the 8051's unique data pointer (DPTR) being a 16-bit register, unlike other 8-bit registers.

05:00

🔍 Exploring Register and Direct Addressing Modes

The paragraph delves into register addressing mode, where data is specified using registers like accumulator (A) and registers R0 to R7. It clarifies that in the 8051, certain operations between registers are not allowed, specifically the direct transfer between R0 to R7 registers. Direct addressing mode is also discussed, where the operand's address is included in the instruction itself. Examples are given to illustrate how internal RAM and Special Function Registers (SFRs) are accessed using direct addressing, with addresses ranging from 00h to 7Fh for internal RAM and 80h to FFh for SFRs.

10:00

🔗 Indirect and Indexed Addressing Modes Explained

This paragraph explains indirect addressing mode, where the address of the operand is given by a register, allowing access to both internal and external RAM. The use of the '@' symbol and registers R0 to R7 for accessing internal RAM is detailed, along with the use of the DPTR register for external RAM access using the 'movex' instruction. The paragraph also introduces indexed addressing mode, which is used to access data from code memory in the Harvard architecture of the 8051 microcontroller. The importance of storing non-volatile data in ROM is emphasized, and the use of the 'c' symbol in instructions to access code memory is explained with examples.

Keywords

💡Addressing Modes

Addressing modes in the context of the video refer to the different methods used by the 8051 microcontroller to specify operands in an instruction. They are fundamental to understanding how the microcontroller processes instructions and accesses data or memory locations. The video explains five addressing modes, each with its own syntax and use case, which are crucial for programming and controlling the microcontroller effectively.

💡Microcontroller 8051

The Microcontroller 8051 is a specific type of microcontroller that was introduced by Intel in 1981. It is an 8-bit microcontroller with an architecture that supports a wide range of applications. In the video, the 8051 is the central topic, and various concepts such as its addressing modes are discussed to educate viewers on how to program and utilize its capabilities.

💡Immediate Addressing Mode

Immediate addressing mode is one of the five addressing modes explained in the video. It involves specifying data directly within the instruction itself, preceded by a '#' symbol. This mode is used when the data required for an operation is known at the time the instruction is written. For example, 'MOV A, #15h' moves the immediate data '15h' into accumulator A.

💡Register Addressing Mode

Register addressing mode is used when data is specified by registers, such as accumulator A or registers R0 to R7. The video clarifies that while data can be moved between the accumulator and these registers, direct operations between registers R0 to R7 are not allowed, emphasizing the unique constraints of the 8051 microcontroller.

💡Direct Addressing Mode

In direct addressing mode, the operand's address is explicitly stated in the instruction. This mode is used for accessing data stored in specific memory locations, such as internal RAM or Special Function Registers (SFRs). The video provides examples like 'MOV A, 35h', which moves data from the memory location '35h' into accumulator A.

💡Indirect Addressing Mode

Indirect addressing mode uses a register to provide the address of the operand. This mode is versatile as it allows access to both internal and external RAM through registers. The video script mentions using '@' with 'R1' as an example, where the content of 'R1' is treated as an address to access data in internal RAM.

💡External RAM

External RAM refers to memory locations outside the microcontroller's internal memory. The video discusses accessing this memory using 16-bit addressing with the DPTR (Data Pointer) register and also 8-bit addressing with registers like R0 to R7, which requires padding zeros for the upper 8 bits of the address.

💡Internal RAM

Internal RAM is the memory within the microcontroller itself, which is used for storing data locally. The video explains that internal RAM has a limited range from '00h' to '7Fh' and is accessed using direct or indirect addressing modes.

💡Indexed Addressing Mode

Indexed addressing mode is used to access data from code memory, which is part of the Harvard architecture of the 8051 microcontroller. This mode is essential for accessing non-volatile data stored in ROM, such as ASCII data for display purposes. The video illustrates this with 'MOVC A, @A+DPTR', which accesses code memory at an address calculated by adding the value in accumulator A to the value in the DPTR register.

💡Accumulator

The accumulator is a specific register in the 8051 microcontroller used for arithmetic and logical operations. It is often involved in data transfer operations, as shown in the video when explaining various addressing modes, such as moving data into or out of the accumulator using instructions like 'MOV A, R2'.

💡Special Function Registers (SFRs)

Special Function Registers are a set of registers in the 8051 microcontroller that have specific functions, such as controlling I/O ports or the timer. The video mentions that direct addressing mode can be used to access these registers, with '80h' being an example address allocated to port zero.

Highlights

Introduction to addressing modes in microcontroller 8051.

Explanation of what addressing modes are and their role in specifying operands in instructions.

Introduction of five addressing modes available in the 8051 microcontroller.

Immediate addressing mode explained, including the use of the hashtag symbol before data.

Example of immediate addressing mode with the use of hex data in instructions.

Differentiation between data pointer (DPTR) and other 8-bit registers in 8051.

Register addressing mode explained, with the use of registers A and R0 to R7.

Limitation in 8051 regarding the use of registers with each other in register addressing mode.

Direct addressing mode explained, with the inclusion of specific addresses in instructions.

Examples of direct addressing mode using internal RAM and SFR addresses.

Indirect addressing mode explained, with the use of registers to point to operand addresses.

Use of internal RAM and external RAM with indirect addressing mode.

External RAM addressing with the use of DPTR and the MOVEX instruction.

8-bit addressing in external RAM using registers R0 to R7 and the MOVEX instruction.

Index addressing mode for accessing data from code memory in the Harvard architecture.

Explanation of the use of the 'C' in instructions for index addressing mode.

Clarification of addressing modes for internal and external ROM and RAM.

Invitation for viewers to ask questions if they have any confusion regarding addressing modes.

Transcripts

welcome to engineering funda family this

video is a part of

microcontroller8051 video lecture series

and in this video i'll be going to

explain you

addressing modes of microcontroller 8051

let me explain you first what is the

meaning of addressing modes

see addressing mode means what it is a

way of specifying operands in

instruction so when you write any

instruction in that obviously you will

be having operands

those operands may be data it may be

resistor it may be memory location right

so how to specify operands that is

defined by addressing modes so with

eight zero five one microcontroller we

have five addressing modes i'll explain

you each and every addressing modes

along with examples so that will gives

you more clarity let us see all those

things step by step

so my dear students when we talk about

addressing modes then you should know

various formats of specifying operands

in instruction is referred as addressing

mode

here

when we talk about immediate addressing

mode

then in immediate addressing mode we

specify

data in instruction itself

that data may be of one byte or two byte

here my dear students when you write

data at that time you will have to write

hashtag

before data

so once you write hashtag after that you

have to mention data right whatever data

that you want to specify

let me give you example so here for

example when you write mu a comma

hashtag 15 hacks

then what you are doing

this 15 hex data which is specified in

this instruction that you are copying

inside resistor a

when you write move dptr comma hashtag

1000 hex

then what you do is here this 1000 hex

data that you are copying inside dptr

and one more thing that you need to note

down

see

with 8051 we just have this dpdr

resistor in which directly we can have

16 bits other resistors are having size

of 8 bits only right

so here when you specify data

like this hashtag then 15 hacks

or you can say

here we have two bytes data

that is having same format hashtag then

two byte data and then hacks so this is

how we can represent this immediate data

in instruction that's why it is referred

as immediate addressing mode

now i'll explain you resistor addressing

mode so from name itself you can

understand

see here you will be specifying data by

resistors right

in instruction you will be specifying

data by resistor only

here

you will be using this resistors only

like a and r0 to r7 so these resistors

that we will be using

here my dear students for example when

you write mu a comma r2 then what you

are doing you are copying r2 inside a

when you write mu r2 comma a then what

you are doing you are copying the

content of a into r2 so that is how we

specify

data inside resistor and then you are

performing

operations based on resistors only right

like when you write move r1 comma r2

then you will be thinking like you will

be copying r2 inside r1 right but my

dear students this is not allowed with

eight zero five one why the reason is

you will have to use

accumulator in terms of resistor

addressing mode you cannot use r0 to r7

resistor with each other

right so that is how things are there

with 805 1 this is not allowed that's

why specifically i have mentioned this

instruction many of the time students

are asking me like sir i am having error

and they are writing it like this and if

you write instructions like this

definitely you will be finding errors

right so you are not allowed to do this

now my dear students when you talk about

direct addressing mode then in that

addressing mode

address of operand will be given in

instruction

so here you will be giving address of

operand remember this

here

you are using internal ram or sfr

address right internal ram address is

there from 0 0 hex to 7 half x

and sfr address that is there from eight

zero hex to ff hacks so that is what we

are using it with direct addressing mode

let me give you some example like when

you write move a comma 35 hacks then

what you are doing here you see you have

not written hashtag see here when you

write hashtag then that is immediate

data but when you don't write hashtag

means this is address

and this is what ram address right

now ram address is there in between 0 to

7 f that's why i'm saying it is ram

address

sfr address that is there from 8 0 hex

to ffx

so when you write

a comma 35

means here my dear students this 35 is

address and at this address

whatever data is there inside ram that

is internal ram right that will be

copied inside

accumulator a that is how it is

happening

when you execute move a comma 8 0 hex

what you are doing

you are copying

the content of 8 0 hex address eight

zero hex that is what allocated with

port zero right

so here my dear students when you write

a comma eight zero means eight zero

hacks is address

and for that whatever content is there

that you will be copying it inside

accumulator a

right

for example when you write move

3 0 hex comma 3 5 hex then what you are

doing

see 3 5 hacks that is also address over

here and three zero hex that is also

address

and

both address are having some data

right so now what will happen after this

instruction 35 hex address is having

whatever data that you will be copying

it inside

three zero hex address that is how this

instruction is happening right

now my dear students i'll explain you

indirect addressing mode so in indirect

addressing mode

address of

operand will be given by resistor so

here with

internal ram we have resistors as well

as sfrs are also resistors so address of

operand will be given by resistor now

you will be not using direct addressing

right like we have written direct

address over here

if you can remember direct address of

different sfr that is good but if you

cannot remember direct address then you

can use resistors right so here internal

ram external ram can be accessed by this

mode

and here for example when you write

this

indirect addressing mode with the use of

at the rate at that time my dear

students you will be using internal ram

remember this

and here when you write move a comma at

the rate r1 then what you are doing

this r1 is having whatever data now that

is address

and at that address whatever data is

there with internal ram that you will be

copying it inside a so obviously r1 can

be there with the value in between 0 to

7 f remember this right

internal ram is there from the range of

0 0x to 7f hex so r1 can be pointing any

data inside that internal ram and that

data will be copied inside a

here when you write move at the rate r2

comma a then what you are doing is you

are moving content of a

at the memory location pointed by

resistor r2 right and obviously as i

have told you now r2 that is pointing

what internal ram right so r2 must be

there in between 0 0 to

7 f hex then only you can use this at

the rate

now my dear students

for external ram you will be having

16 bits of addressing by dbtr and for

that you'll have to use x you see here

normal move was there but now you will

be using movex

so in that situation what you are doing

is you are using external ram

and how to use that by using dbtr data

pointer resistor that is pointing

external ram only right so you can

directly use it by using data pointer

how you see when you write move x a

comma at the red db tr then dptr is a

pointer which is pointing external ram

at that location whatever data is there

that you will be copying inside

accumulator a

when you write mu x

at the rate dbt or comma a then what you

are doing you are copying the content of

a

at the memory location pointed by dpdr

right

so external ram that we can access by

using dbtr but along with that you will

have to use x in move instruction

now my dear students i'll explain you

external ram with 8 bits of addressing

so 8 bits of addressing is possible

using external ram

in that you can use any resistor like r0

to r7

but here there are few basic things that

you need to note down

see external ram that is having address

of 16 bits here 8 bits that we are using

by resistor

so external ram is been accessed that's

why move x that you'll have to write

first

then when you write a comma at the rate

r1

then

external ram address that is been

pointed by r1 but how you see

if value of r1 is 25 hex then initial

two digits of this hex that should be 0

means 0 0 to 5 hex that will be my

address that was pointed by r1 in terms

of 16 bits and at that

location whatever content is there that

you will be copying inside accumulator

right so here my dear students you can

use eight bits but by default

assembler will convert that address in

terms of 16 bits by adding eight

zeros over here in terms of binary

for example when you write mu x at the

rate r0 comma a then you will be copying

the content of a

at the memory location pointed by r0 in

external ram remember this as you are

writing x over here it will be external

ram only but in external ram

see

this r0 contain 35 hex if it is like

this then initial two hex digits that

will be 0 as per

this

external ram operation for external ram

you will have to write x over here

remember this normally we use dbtr

resistor only but as if you use other

resistor then it will be padding zeros

like this that is how things are

happening now i'll explain you index

addressing mode

here this mode is been used to access

data from code memory you should know my

dear students8051

that is based on harvard architecture so

in harvard architecture we have

separate memory for data and code

code is there with rom

and data is there with ram right but

in some situation you may need to store

those data which are not volatile

for example if i say ascii data then

ascii data should not be volatile data

so that should be stored inside rom for

example seven segment display that you

are interfacing so that is also

non-volatile data that also you need to

store inside rom so those data which are

not volatile that you must store inside

rom as ram is volatile memory so when

you restart system the data of ram will

get vanished right so that you must need

to store inside

rom only

and for that you will have to use index

addressing mode in

instructions so here when you write c

at that time you will be using index

addressing mode let me explain you that

so you see here move and then see that

i'm writing

right so mosi means what you are using

code memory

right and how you see a comma at the

rate a plus dbtr what it means

a plus dbtr now that is my address and

at that address whatever content is

there that you are copying it inside

accumulator a

for example when you write move c a

comma at the red a plus b c so what you

are doing

you are having

address which is a plus pc

and at that location whatever content is

there inside rom remember this it is

there inside rom

so inside rom whatever content is there

that you are copying it inside

accumulator a so when you write c at the

time you will be using code memory means

it will be internal or external rom and

when you write x at that time you will

be using external ram

and when you don't write anything at the

time you will be using internal ram

which is having size of 0 0 to

7 f hex that is how all the addressing

modes are there

so i think now it is clear to you how

addressing modes are there still if any

confusion is there just post that in

common box i'll be happy to help you

thank you so much for watching this

video