Microcontroller- An overview

M.SARASWATHI
Associate Professor
Department of ECE
Panimalar Engineering College
MICROCONTROLLER PROGRAMMING - AN OVERVIEW
A Webinar on

Contents
1. Why programming is important?
2. Input and Output devices for
microcontroller
3. Application of Microcontroller
4. Interfacing Keypad with
microcontroller
5. Keypad Matrix Scanning concept.
6. ALP for interfacing keypad with
LCD.
2

Why Programming is important?
There are three types or levels of
Programming Languages for
8051 Microcontroller.
1. Machine Language
2. Assembly Language
3. High-level Language
Programming in the sense of Microcontrollers means writing
a sequence of instructions to perform a predefined task.
3
 Toys movement of Left,
Right – both legs and
hands is Predefined Task

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5

 Assembly Language is a pseudo-English representation
of the Machine Language.
 The 8051 Microcontroller Assembly Language is a
combination of English like words called Mnemonics
and Hexadecimal codes.
 It is also a low level language and requires extensive
understanding of the architecture of the Microcontroller.
Why Assembly Language?
6

 The Programs written in Assembly gets executed faster and
they occupy less memory.
 With the help of Assembly Language, you can directly
exploit all the features of a Microcontroller.
 Using Assembly Language, you can have direct and
accurate control of all the Microcontroller’s resources like
I/O Ports, RAM, SFRs, etc.
 Compared to High-level Languages, Assembly Language
has less rules and restrictions.
Advantage of Assembly Language Programming
7

Input and Output devices for microcontroller
8

APPLICATION OF MICROCONTROLLER
9

 Hex key pad is essentially a collection of 16 keys
arranged in the form of a 4×4 matrix.
 Hex key pad usually
have keys representing
numeric 0 to 9 and
characters A to F.
HEX KEYPAD (or) 4x4 MATRIX
10

 The hex keypad has 8 communication lines namely R1,
R2, R3, R4, C1, C2, C3 and C4.
 R1 to R4 represents the four rows.
 C1 to C4 represents the four columns.
 When a particular key is pressed the corresponding row
and column to which the terminals of the key are
connected gets shorted.
11

 The program identifies which key is pressed by a
method known as column scanning.
 In this method a particular row is kept low (other rows
are kept high) and the columns are checked for low.
 If a particular column is found low then that means that
the key connected between that column and the
corresponding row (the row that is kept low) is been
pressed.
For example :
If row R1 is initially kept low and column C1 is found
low during scanning, that means key ‘1’ is pressed.
12

Input
O
U
T
P
U
T
Case 1:
Case 2:
 5v is individually connected to all keys
13

 Initially keep all values as 1.
Input
O
U
T
P
U
T
14

Input
O
U
T
P
U
T
 ROW1 And COLUMN1 IS PRESSED THE KEY IS ‘1’
(R1,C1)
15

Interfacing Keypad with 8051
16

COLUMN SCANNING
INPUT ROW - PORT 1.3 to 1.0
R4 to R1
8051
R1=0
INPUT =1110= EH
C1=0: 1110=EH; Display = ‘1’
C2=0: 1101=DH; Display = ‘2’
C3=0: 1011=BH ;Display = ‘3’
C4=0: 0111=7H ;Display = ‘A’
COLUMN OUTPUT
PORT 1.7 to 1.4
C4 to C1
18

COLUMN SCANNING
R4 to R1
8051
R2=0
INPUT =1101= DH
C1=0: 1110=EH ;Display = ‘4’
C2=0: 1101=DH ;Display = ‘5’
C3=0: 1011=BH ;Display = ‘6’
C4=0: 0111=7H ;Display = ‘B’
COLUMN OUTPUT
PORT 1.7 to 1.4
C4 to C1
19

COLUMN SCANNING
R4 to R1
8051
R3=0
INPUT =1011= BH
COLUMN OUTPUT
PORT 1.7 to 1.4
C4 to C1
C1=0: 1110=EH;Display= ‘7’
C2=0: 1101=DH;Display= ‘8’
C3=0: 1011=BH;Display= ‘9’
C4=0: 0111=7H;Display= ‘C’
20

COLUMN SCANNING
R4 to R1
8051
R4=0
INPUT =0111= 7H
COLUMN OUTPUT
PORT 1.7 to 1.4
C4 to C1
C1=0: 1110=EH;Display= ‘E’
C2=0: 1101=DH;Display= ‘0’
C3=0: 1011=BH;Display= ‘F’
C4=0: 0111=7H;Display= ‘D’
21

ASCII LOOK UP TABLE FOR ROW( COLUMN SCANNING)
ORG 300H
Code1: DB ‘0’, ‘1’, ‘2’, ‘A’ ; Row1
Code2: DB ‘4’, ‘5’, ‘6’, ‘B’ ; Row2
Code3: DB ‘7’, ‘8’, ‘9’, ‘C’ ; Row3
Code4: DB ‘E’, ‘0’, ‘E’,‘D’ ; Row4
(OR)
22

Digit A B C D E F G DP
0 1 1 1 1 1 1 0 0
1 0 1 1 0 0 0 0 0
2 1 1 0 1 1 0 1 0
3 1 1 1 1 0 0 1 0
4 0 1 1 0 0 1 1 0
5 1 0 1 1 0 1 1 0
6 1 0 1 1 1 1 1 0
7 1 1 1 0 0 0 0 0
8 1 1 1 1 1 1 1 0
9 1 1 1 1 0 1 1 0
ASCII LOOK UP TABLE FOR ROW( COLUMN SCANNING)
23

Digit A B C D E F G DP
A 1 1 1 0 1 1 1 0
B 0 0 1 1 1 1 1 0
C 1 0 0 1 1 1 0 0
D 0 1 1 1 1 0 1 0
E 1 0 0 1 1 1 1 0
F 1 0 0 0 1 1 1 0
24

LUT:
DB 0 1 1 0 0 0 0 0
DB 1 1 0 1 1 0 1 0
DB 1 1 1 1 0 0 1 0
DB 1 1 1 0 1 1 1 0
DB 0 1 1 0 0 1 1 0
DB 1 0 1 1 0 1 1 0
DB 1 0 1 1 1 1 1 0
DB 0 0 1 1 1 1 1 0
DISPLAY OF LCD DEVICE
 Label DB can be called as a Look Up Table (LUT).
 Label DB is known as Define Byte – which defines 8 Bit.
25

DB 1 1 1 0 0 0 0 0
DB 1 1 1 1 1 1 1 0
DB 1 1 1 1 0 1 1 0
DB 1 0 0 1 1 1 0 0
DB 1 0 0 1 1 1 1 0
DB 1 1 1 1 1 1 0 0
DB 1 0 0 0 1 1 1 0
DB 0 1 1 1 1 0 1 0
26

1. Initializes PORT 0 as an output port by writing all 0’s to
it
2. PORT 1 as an input port by writing all 1’s to it.
3. Then make Row 1 ‘Low’ by clearing P1.0 and scan the
columns one by one for low using JB instruction.
4. If column C1 is found ‘Low’, that means KEY ‘1’ is
pressed.
5. Accumulator is loaded by zero (A=0) and DISPLAY
subroutine is called.
ABOUT THE PROGRAM
27

6. The display subroutine adds the content in A with the
starting address of LUT stored in DPTR (A+DPTR).
7. Load A with the data to which the resultant address
points (using instruction MOVC A,@A+DPTR).
8. The present data in A will be the digit drive pattern for
the current key press.
9. This pattern is put to Port 0 for display.
10. This way the program scans for each key one by one
and puts it on the display if it is found to be pressed.
28

PROGRAM:
ORG 00H
MOV DPTR,#LUT ; moves starting address of LUT to DPTR
MOV A,#11111111B ; loads A with all 1's
MOV P0,#00000000B ; initializes P0 as output port
BACK: MOV P1,#11111111B ;loads P1 with all 1's
CLR P1.0 ;makes row 1 low
JB P1.4,NEXT1 ;checks whether column 1 is low and
//jumps to NEXT1 if not low
MOV A,#0D ; loads a with 0D if column is low (that
//means key 1 is pressed)
ACALL DISPLAY ;calls DISPLAY subroutine
NEXT1: JB P1.5,NEXT2 ; checks whether column 2 is
// low and so on...
MOV A,#1D
ACALL DISPLAY
29

NEXT2: JB P1.6,NEXT3
MOV A,#2D
ACALL DISPLAY
MOV A,#3D
ACALL DISPLAY
NEXT4: SETB P1.0
CLR P1.1
JB P1.4,NEXT5
MOV A,#4D
ACALL DISPLAY
MOV A,#5D
ACALL DISPLAY
30

MOV A,#6D
ACALL DISPLAY
MOV A,#7D
ACALL DISPLAY
NEXT8: SETB P1.1
CLR P1.2
JB P1.4,NEXT9
MOV A,#8D
ACALL DISPLAY
MOV A,#9D
ACALL DISPLAY
31

MOV A,#10D
ACALL DISPLAY
MOV A,#11D
ACALL DISPLAY
NEXT12: SETB P1.2
CLR P1.3
JB P1.4,NEXT13
MOV A,#12D
ACALL DISPLAY
MOV A,#13D
ACALL DISPLAY
32

MOV A,#14D
ACALL DISPLAY
NEXT15: JB P1.7,BACK
MOV A,#15D
ACALL DISPLAY
LJMP BACK
DISPLAY: MOVC A,@A+DPTR ; gets digit drive pattern for
//the current key from LUT
MOV P0,A ;puts corresponding digit drive
//pattern into P0
RET
33

LUT:
DB 01100000B // Look up table starts here
DB 11011010B
DB 11110010B
DB 11101110B
DB 01100110B
DB 10110110B
DB 10111110B
DB 00111110B
DB 11100000B
DB 11111110B
DB 11110110B
DB 10011100B
DB 10011110B
DB 11111100B
DB 10001110B
DB 01111010B
END
34

Microcontroller- An overview

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