Switches and LEDs interface to the 8051 microcontroller

Switches and LEDs Interface to the 8051
Microcontroller
Prepared by:
Afrah Salman

Switch Basics
• A switch is an electrical component that can break an electrical
circuit, interrupting the current or diverting it from one
conductor to another.
• If we directly connect a switch to one of the microcontroller port
pins, the pin floats when the switch is open. Meaning, it is not at
a fixed logic level 0v or 5v.

Interfacing Switch
• Fig. 1 shows how to interface the switch to microcontroller. A simple
switch has an open state and closed state. However, a
microcontroller needs to see a definite high or low voltage level at a
digital input. A switch requires a pull-up or pull-down resistor to
produce a definite high or low voltage when it is open or closed. A
resistor placed between a digital input and the supply voltage is
called a "pull-up" resistor because it normally pulls the pin's voltage
up to the supply.

Fig.1InterfacingswitchtoMicrocontroller

LED Basics
• Light Emitting Diodes are the semi conductor light sources.
Commonly used LEDs will have a cut-off voltage of 1.7V and
current of 10mA. When an LED is applied with its required
voltage and current it glows with full intensity. The Light
Emitting Diode is similar to the normal PN diode but it emits
energy in the form of light. The color of light depends on the
band gap of the semiconductor.

Interface to the Microcontroller
• Now we could go ahead and interface it to the
microcontroller, but we would rather interface 8 switches
and 8 LED's to two ports as shown in the schematic below.

• As we can see the schematic has basic circuits for
oscillator, reset and power connections for the
microcontroller.
• A DIP (dual in line package) Switch, array of 8
switches is connected to PORT3 AND 8 LEDs
toPORT2.
• Observe the RR1 component, it is array of 8 resistors
in a single pack(SIP). It is as good as connecting 8
pull-up resistors as shown in figure 1. You could also
use 8 discrete resistors as well.

Interfacing Switch with 8051
• We now want to control the LED by using switches in 8051 Slicker
Board. It works by turning ON a LED & then turning it OFF when
switch is going to LOW or HIGH. The 8051 Slicker board has eight
numbers of point LEDs, connected with I/O Port lines (P0.0 – P0.7)
to make port pins high. Eight switches, connected with I/O port
lines (P2.0 – P2.7) are used to control eight LEDs.

Circuit Diagram to Interface Switch with 8051

Example1:The following program will make the value of PIN3.1 keeps
toggling (ON/OFF) after some delay.
org 00H
;MAIN PROGRAM
Toggle: MOV P3, #01H ;move 00000001 to PORT3
CALL delay ;execute delay
MOV A, P3 ;move PORT3 value to
accumulator
CPL A ;complement PORT3 value
MOV P3, A ;move 11111110 to PORT3
CALL delay ;execute delay
SJMP Toggle

;DELAY SUB-ROUTINE
delay: MOV R5, #10 ;load register R5 with 10
third: MOV R6, #200 ;load register R6 with 200
second: MOV R7, #200 ;load register R7 with 200
DJNZ R7, $ ;decrement R7 till it is zero
DJNZ R6, second ;decrement R6 till it is zero
DJNZ R5, third ;decrement R5 till it is zero
ret ;go back to main program
END

Example2:Aswitch is connected to pin PI .7. Write a program to check the
status of SW and perform the following:
If SW=0, send letter ‘N’ to P2., If SW=1, send letter ‘Y’ to P2.
org 00H
;MAIN PROGRAM
SETB P1.7 ;make P1.7 an input
AGAIN: JB P1.2, OVER ;jump if P1.7=1
MOV P2, #’N’ ;SW=0, issue ‘N’ to P2
SJMP AGAIN ;keep monitoring
OVER: MOV P2,#’Y’ ;SW=1, issue ‘Y’ to P2
SJMP AGAIN ;keep monitoring

Example3:Aswitch is connected to pin PI .7 and an LED to pin P2.7. Write
a program to get the status of the switch and send it to the LED.
org 00H
;MAIN PROGRAM
SETB P1.7 ;make P1.7 an input
AGAIN: MOV C,P1.0 ;read the SW status into CF
MOV P2.7, C ;send the SW status to LED
SJMP AGAIN ;keep repeating
Note: The instruction “MOV P2.7, P1.0” is wrong since such an
instruction doesn’t exist. However, “MOV P2, P1” is a valid instruction.

Switches and LEDs interface to the 8051 microcontroller

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Switches and LEDs interface to the 8051 microcontroller

Similar to Switches and LEDs interface to the 8051 microcontroller (20)

More from University of Technology - Iraq

More from University of Technology - Iraq (19)

Recently uploaded

Recently uploaded (20)

Switches and LEDs interface to the 8051 microcontroller