VTech Alphabert s Magic Readport User Manual download pdf (Page 26)

Lab Manual of Microcontroller & Interfacing Page 26

EXPERIMENT NO. 6

AIM: Write a program to generate square wave of 50% duty cycle having frequency 5 KHz at

port pin P1.0 using timer 1 in mode 2. Modify program to generate pulse waveform of

70% duty cycle using timer on the same pin.

Calculation of delay:

Time = 1/Frequency = 1/(5x10

) = 200 µS

For 50% duty cycle ON time and OFF time are equal

= T

OFF

= 100 µS

Time delay required is 100.

If we consider crystal frequency 12 MHz, time to execute one cycle is

T = = 1 µS

If we will use pure software delay to generate delay of 100 µS

Program:

ORG 00h ; Start program from location 00h

CLR P1.0 ; Make P1.0 output pin

next: ACALL delay ; Call delay of 100 µS

CPL P1.0 ; Complement P1.0 to generate square wave

SJMP next

delay: MOV R7,#30h ; Load count value 48 (30h)

loop: DJNZ R7, loop ; Decrement R7 until it becomes zero

NOP ; No operation

RET ; Return to main routine

END

Total number of cycles in delay loop:

Total number if cycles C

= C

+ C

= 1 + 4 8⤬2 + 1+2 = 100

Where, C

= Number of cycles outside the loop

= Number of cycles inside the loop

= Number of cycles for return instruction.

Total time = C

x 1 µS = 100 µS

Note: Execute this program using Keil and observe waveforms at port pin P1.0. (Measure

frequency and verify whether it is giving correct value or not)

:: WORKSHEET ::

Exercise:

A. Modify program for 80% duty cycle.

Hint: Use separate delay loop for ON time and OFF time. Total time is 200 µS, so use

160 µS for ON time and 40 µS for OFF time. You can also prepare delay

subroutine of 10 µS. Call delay subroutine 16 times for ON time and 4 times for

OFF time.

Memory

Location

HEX

code

Label Opcode Operands Comments

1 2 ... 21 22 23 24 25 26 27 28 29 30 31 ... 79 80

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VTech Alphabert s Magic Readport User Manual Page 26

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