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8051 Microcontroller: Internals, Instructions,Programming and Interfacing by Subrata Ghoshal

Chapter - 7

Programming Examples - I

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Example 1: Copy Block

R0 may be used as source pointer and R1 as

destination pointer.

R7 may be used as counter.

Data may be copied from source to destination

through the accumulator.

01 OF 33

Copy a block of twenty bytes of data available

from address 60H to 73H to the location starting

from 40H.

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Example 1 (continued)

Direct copy from one address to another needsmultiple instructions.

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Algorithm

Step 1: Initialize R0 as source and R1 as destination

pointers and load R7 by 20d to serve as the counter.

Step 2: Copy a byte from source to destination usingR0 and R1 through accumulator (as temporary

storage). Update pointers after copying.

Step 3: Decrement counter by one. Continue at Step 2

if counter is not zero.

Step 4: Terminate the process.

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Software

START: MOV R0, #60H ; start source

MOV R1, #40H ; start destination

MOV R7, #14H ; counter of 20d

COPYIT: MOV A, @R0 ; get a byte

MOV @R1, A ; save it

INC R0 ; next source

INC R1 ; next destinationDJNZ R7, COPYIT ; continue

OVER: SJMP OVER ; done

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Example 2 : Shift Block

R0, R1 and R7 may be source and destination

pointers and counter, respectively.

Shifting must be started from 57H and not from 50H,

otherwise data would be destroyed.

Shift a block of eight bytes of data, presently

located from 50H to 57H, one byte up, so that

the data is available from 51H to 58H.

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In shift-block, overlapping exists but not in copy-block.

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Algorithm

Step 1: Initialize R0 as source and R1 asdestination pointers for highest addresses and

load R7 by 08H as counter. Step 2: Copy a byte via accumulator from

source to destination using R0 and R1 andthen decrement both pointers by one.

Step 3: Decrement counter by one. Continue atStep 2 if counter is not zero.


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Software

START: MOV R0, #57H ; point source

MOV R1, #58H ; point destination

MOV R7, #08H ; counter for 8SHIFT: MOV A, @R0 ; get a byte

MOV @R1, A ; save it

DEC R0 ; next source

DEC R1 ; next destination

DJNZ R7, SHIFT ; continue

OVER: SJMP OVER ; terminate

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Example 3: Count No. of nulls

In the worst case, there may not be a single nullbyte or all twenty bytes may be containing 00H.

Twenty bytes of data stored in location from 7FH

to 6CH of internal RAM. Count the number of

those bytes, which contain 00H and store thisnumber of null bytes in RAM location 6BH.

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(a) (b) and (c) may be three possible situations.

(d) Indicates register allotment.

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Algorithm

Step 1: Initialize R0 as source pointer and R7 as

byte counter. Clear accumulator.

Step 2: Compare a byte with zero through pointer.Increment accumulator by one if it is zero.

Step 3: Decrement both pointer and counter by

one. Continue at Step 2 if counter is not zero.

Step 4: Save accumulator content through pointer.

Terminate the process.

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Software

START: MOV R0, #7FH ; max address

MOV R7, #14H ; byte counter

MOV A, #00H ; null counterMAIN: CJNE @R0, #00H, NOTNUL ; compare

INC A ; null byte, increment count

NOTNUL: DEC R0 ; point next location

DJNZ R7, MAIN ; complete checking

MOV @R0, A ; save null count at 6BH

OVER: SJMP OVER ; terminate program

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Example 4: Find Checksum

Checksums are generally used to ensure thecorrectness of a set of communicated data.

Sixteen consecutive bytes starting from 50H are

having unsigned integers. Develop a program to

add all these sixteen integers and store the 8-bit

sum in memory location 60H

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Algorithm

Step 1: Initialize R0 as source pointer and load R7 by

16d to serve as the counter. Clear the accumulator to

calculate the sum.

Step 2: Add one byte with accumulator as pointed by

R0. Then increment pointer by one.

Step 3: Decrement counter by one. Continue at Step 2

if counter is not zero.

Step 4: Store accumulator as pointed by R0.

Terminate the process.

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Software

START: MOV R0, #50H ; point first entry

MOV R7, #10H ; counter with 16d

MOV A, #00H ; clear checksumADDIT: ADD A, @R0 ; add one number

INC R0 ; point next

DJNZ R7, ADDIT ; continueMOV @R0, A ; save checksum at 60H


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Example 5: Sum of Natural Numbers

We select bank #0 so that its R6 may

be address by direct addressing also.

Write a program to generate and store natural

numbers starting from 1 up to N terms and also

find the sum of it. Assume the value of N is storedin location 30H. Store generated natural

numbers from 40H. Leave the sum in the

accumulator.

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R7: Term

counter

R6: Generated

natural number

A: Sum

R0: Storagepointer

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Algorithm

Step 1: Select bank #0. Initialize R0 as storage pointer

of generated natural numbers and load R7 from 30H

by N to serve as counter. Clear R6 and accumulator.

Step 2: Increment R6 by one to generate the next

natural number. Save it through R0 and add it with

accumulator. Then increment R0 to point next.

Step 3: Decrement R7 by one and continue at Step 2 ifR7 is not zero.


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Software

START: MOV PSW, #00H ; select bank #0

MOV A, #00H ; initialize sun

MOV R6, #00H ; for natural number

MOV R0, #40H ; storage pointerMOV R7, 30H ; load counter

MAIN: INC R6 ; next natural number

MOV @R0, 06H ; save generated number

ADD A, R6 ; update sumINC R0 ; next saving pointer

DJNZ R7, MAIN ; continue


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Example 6: Sum of a Series

The odd numbers are positive and

even numbers are negative.

Write a program to find the sum of the series

12 + 34 + up to N terms.

Assume the non-zero value of N is available in

location 30H. Store the sum in the accumulator.

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Algorithm

Step 1: Select bank #0. Load R7 by N from 30H as counter.Clear R6 and accumulator.

Step 2: Increment R6 by one to generate next (odd) natural

number. Add it with accumulator. Step 3: Decrement counter R7 by one. Continue at Step 4 if

counter is not zero. Otherwise go to Step 6.

Step 4: Increment R6 by one to generate next (even) naturalnumber. Clear carry flag by loading 00H in PSW. Thensubtract the generated number from the accumulator.

Step 5: Decrement counter R7 by one. Continue at Step 2 if it isnot zero.

Step 6: Terminate the program.

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Software (part 1)

START: MOV PSW, #00H ; select bank #0

MOV A, #00H ; clear sum

MOV R6, #00H ; term startingMOV R7, 30H ; load counter by N

MAIN: INC R6 ; get next odd term

ADD A, R6 ; add odd termDJNZ R7, NEXT ; check for N

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Software (part 2)

SJMP OVER ; N terms added

NEXT: INC R6 ; next even term

MOV PSW, #00H ; clear carry

SUBB A, R6 ; subtract even term

DJNZ R7, MAIN ; continueOVER: SJMP OVER ; terminate

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Example 7: Fibonacci series

Fibonacci series

Generate Fibonacci series up to N terms and

save from location 50H onwards. Assume N

being available in location 4FH. Also assume thevalue of N to be greater than 3.

0 1 1 2 3 5 8

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R7 : counter for N

R0 : source pointer R1 : destination

pointer

A term generator

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Algorithm

Step 1: Load counter R7 by N from 4FH.

Step 2: Load R0 by 51H and store 01H (2nd Term).

Step 3: decrement R0 by 1 and store 00H (1st Term).

Step 4: Load R1 by 52H (location of 3rd Term). Also decrement

R7 by 2 as two terms generated.

Step 5: Load A through R0. Increment R0 by one.

Step 6: Add the term pointed by 0 with A. Store it through R1.Then increment R1 by 1.

Step 7: Decrement R7 by one and if not zero then Step 5

Step 8: terminate program.

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Software (part 1)

START: MOV R7, 4FH ; load counter by N

MOV R0, #51H ; point 2nd Term

MOV @R0, #01H ; store 2nd

TermDEC R0 ; point 1st Term

MOV R0, #00H ; store 1st Term

MOV R1, #52H ; point 3rd

TermDEC R7

DEC R7 ; two terms generated

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Software (part 2)

MAIN: MOV A, @R0 ; get one term

INC R0 ; point next term

ADD A, @R0 ; add two termsMOV @R1, A ; save new term

INC R1 ; point next new term

DJNZ R7, MAIN ; continue


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Example 8: Generate a Series

This is superimposition of two series.

Generate and store the following series

up to N terms. Value of N is available

in location 30H. The series is presentedin decimal number system.

1 2 3 11 12 13 21 22 23 31

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Flowchart

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Software (part 1)

START: MOV R7, 30H ; load counter by N

MOV A, #01H ; first term in A

MOV R0, #40H ; storage areapointer

MAIN: MOV R6, #03H ; term counter

MAIN1: MOV @R0, A ; save one termDJNZ R7, NEXT ; continue

SJMP OVER ; terminate

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Software (part 2)

NEXT: INC A ; next number

DJNZ R6, MAIN1 ; max 3 times

MOV R6, #07H ; count gaps

NEXT1: INC A ; next number

DJNZ R6, NEXT1 ; count 7 gaps

SJMP MAIN ; loop again


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8051 Microcontroller: Internals InstructionsP i d I f i b S b Gh h l

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