03a Digital Ouput- Digital Ouputs - Light Emitting Diodes

8/3/2019 03a Digital Ouput- Digital Ouputs - Light Emitting Diodes

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Digital Outputs

Light Emitting Diodes (LEDs)

Updated 2007


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CCS C Instructions for I/O Pins output_low (pin): Sets a given pin to the ground state. output_high (pin): Sets a given pin to the high state. output_toggle(pin): Toggles the high/low state of the specified pin. output_bit (pin, value): Outputs the specified value (0 or 1) to the specified

I/O pin.

output_X (value): Output an entire byte to a port. output_float (pin): Sets the specified pin to the input mode. output_drive(pin): Sets the specified pin to the output mode.

value = input (pin): Returns the state of the indicated pin. value = input_X(): Inputs an entire byte from a port.

port_b_pullups (value):Sets the port B input pullups.

value = get_tris_X(): Returns the value of the TRIS register of port X. set_tris_X (value): Allow the I/O port direction (TRI-State) registers to

be set.


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LEDs in Real Life

Televisions

VCRs

Disk drives

Printers Alarm system control panels


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On/Off Control withPIC16F877A


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PIC


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Cable Wiring


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ElectronicSc

hema

R202

330

VCC

2.LEDB

LOCK

D201

D205

C102

20pF

1.P

ICBLOCK

R203

330

J20

1

9

1011

12

13

14

15

16

1

23

4

5

6

7

8

R208

330

R201

330

SW

7

D202

R205

330

D

207

R206

330

D203

R204

330

R101

100

MCLR/VPP

RA0/AN0

RA1/AN1

RA2/AN2/VREF-/CVREFRA3/AN3/VREF+

RA4/T0CKI/C1OUT

RA5/AN4/SS/C2OUT

RE0/RD/AN5

RE1/WR/AN6

RE2/CS/AN7

VDD

OSC1/CLKI

OSC2/CLKO

RC0/T1OSO/T1CKI

RC1/T1OSI/CCP2

RC2/CCP1

RC3/SCK/SCL

RD0/PSP0

RC4/SDI/SDA

RC5/SDO

RC6/TX/CK

RC7/RX/DT

VDD

RB0/INT

RB1

RB2RB3/PGM

RB4

RB5

RB6/PGC

RB7/PGD

1

2

3

45

6

7

8

9

10

11

13

14

15

16

17

18

19

23

24

25

26

32

33

34

3536

37

38

39

40

D204

D206

R207

330

D208


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Manual vs. Using a Microcontroller

There are two big differences between

changing the connection manually andhaving a microcontroller do it

First, the microcontroller doesnt have to cut

the power when it changes the LED circuitssupply from Vdd to Vss

Second, while a human can make that

change several times a minute, themicrocontroller can do it thousands of timesper second!


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On/Off LED


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Exercise

Make the LED blink on and off once every

three seconds, with the low time twice aslong as the high time

Move on the next slide to compare to what

you have done


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Solution


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Exercise

Make the LED blink 500 milliseconds on and

off 10 times


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Solution


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Example: 8 Bits Counting


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Problem Description

Develop a program to count from 0 to 255

and light up 8 LEDs of the PIC developmentboard according to the binary equivalent ofthe counted decimal number


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Electro

nicSc

hema

VCC

C102

20pF

R201

330

D

207

D201

D206

R205

330

R203

330

R

204

330

1.P

ICBLOCK S

W7

D205

J20

1

9

1011

12

13

14

15

16

1

23

4

5

6

7

8

2.LEDB

LOCK

R208

330

MCLR/VPP

RA0/AN0

RA1/AN1

RA2/AN2/VREF-/CVREF

RA3/AN3/VREF+

RA4/T0CKI/C1OUT

RA5/AN4/SS/C2OUT

RE0/RD/AN5

RE1/WR/AN6

RE2/CS/AN7

VDD

OSC1/CLKI

OSC2/CLKO

RC0/T1OSO/T1CKI

RC1/T1OSI/CCP2

RC2/CCP1

RC3/SCK/SCL

RD0/PSP0

RD1/PSP1

RC4/SDI/SDARC5/SDO

RC6/TX/CK

RC7/RX/DT

VDD

RB0/INT

RB1

RB2

RB3/PGM

RB4

RB5

RB6/PGC

RB7/PGD

1

2

3

4

5

6

7

8

9

10

11

13

14

15

16

17

18

19

20

2324

25

26

32

33

34

35

36

37

38

39

40

R207

330

R101

100

D208

D202

D203

R206

330

R202

330

D20

4


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Cable Wiring

Use a 8 pin ribbon cable to connect PICs

jumpers B0 B7 to LEDs jumpers L0 L7


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C Program


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Exercise

Develop a program to cause an array of 8

LEDs to light up one at a time from left toright


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Solution


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Exercise

Develop a program to cause an array of 8

LEDs to light up one at a time from left toright, then right to left


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Solution


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Lessons Learnt

User requirements drive our code

No duplication code

One task, one function (Modularization)

Use parameters whenever its possible


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Exercise

Develop programs to control the blink of eight

LEDs according to the following patterns Pattern 0:

Pattern 1:

Pattern 2:

Pattern 3:


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References

Microcontroller.

http://www.electronics.netmyne.com/microcontroller.html

PIC Circuits Gallery LED flasher.

http://www.interq.or.jp/japan/se-inoue/e_pic6_1.htm

What's a Microcontroller Student Guide v 2.2.

Parallax 2004

Date post:	06-Apr-2018
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03a Digital Ouput- Digital Ouputs - Light Emitting Diodes

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