VTech Alphabert s Magic Readport User Manual download pdf (Page 49)

BM Dept., Govt. Engg. College, Gandhinagar Page 49

EXPERIMENT NO. 12

AIM: Write a program to measure frequency of external pulses given at the timer 0 input pin.

Display pulses on the LCD connected at port P1.

Circuit diagram:

Interfacing details:

• LCD data lines are connected to port P1.

• Control lines RS (Register select) is connected with port pin P3.0, Enable line connected

with pin P3.1, read/write line connected with P3.2.

• Opto-coupler PC817 is used to provide optical isolation between signal to be measured

and microcontroller. We can connect input signal with amplitude up to 12V to the opto-

coupler. We may connect 230V AC signal by using series resistor of 47K at the input of

opto-coupler. Pulses from the opto-coupler PC817 connected to timer input pin T0.

Program:

;To measure frequency of external pulses using 89C51

;LCD Interfacing details:

;Port 1 Drives data lines, P3.0-RS,P3.1 EN,P3.2 RW

;Signal connected through optocoupler PC817 at pin T0 (P3.4)

ORG 00H

AJMP START

ORG 03H

RETI

ORG 0BH

RETI

ORG 13H

RETI

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VTech Alphabert s Magic Readport User Manual Page 49