EEE3410 Microcontroller Applications Department of Electrical Engineering Lecture 9 Simple I/O Interfacing

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1 Department of Electrical Engineering Lecture 9 Simple I/O Interfacing Week 10 1

2 In this Lecture. Interface 8051 with the following Input/Output Devices Switches Solenoid and relays LEDs Seven Segment Display Dot matrix display 2

3 Introduction The 8051 microcontroller is commonly used for real-world applications, e.g. display control, lighting control, machine control, etc. Various input and output devices are connected to the I/O ports of the microcontroller to deal with different applications. We will introduce some common I/O devices for simple application in this lecture. They are: Mechanical switches Electromagnetic relays Solid-state relays LEDs 7-segment Display Dot Matrix Display 3

4 Mechanical Switches Mechanical switches are common input devices One or more pairs of contacts that can be open or close. Typical switch designations are: SPST (single-pole-single-throw) SPDT (single-pole-double-throw) N.O. SPST N.O. DPST DPDT (double-pole-double-throw) N.O. DPST Normally open (N.O.) contacts close when the switch is activated and normally close (N.C.) contacts close when the switch is activated. 4

5 Connect mechanical switches to 8051 Reset EA V CC XTAL1 XTAL V SS P3.7 P3.6 P3.5 P3.4 SW opens, input to 8051 is HIGH (1) SW closes, input to 8051 is LOW (0) +5V Figure 9.1 SW1 SW2 SW3 SW4 ORG 0000H : JNB P3.7, CASE1 JNB P3.6, CASE2 JNB P3.5, CASE3 JNB P3.4, CASE4 : CASE1: : Check the : status of SW1 : CASE2: : : CASE3: : : CASE4: : : 5

Electromagnetic Relays EEE3410 Microcontroller Applications Electromagnetic relay consists of two parts - solenoid and relay contacts Solenoid is a coil of wire used to produce a magnetic field to

6 Electromagnetic Relays EEE3410 Microcontroller Applications Electromagnetic relay consists of two parts - solenoid and relay contacts Solenoid is a coil of wire used to produce a magnetic field to move a steel actuator where points of contacts are located. The actuator is used to close/open the contact points, such construction is called a relay. Figure 9.2 construction of a Electromagnetic relay 6

7 Driving an Electromagnetic Relays EEE3410 Microcontroller Applications Figure 9.3 show a typical driving circuit of an electromagnetic relay. The transistor will act as a switch to allow current passing through the solenoid. The diode placed across the coil terminal is to protect the transistor damaged from spike voltage during ON/OFF. The external circuit connected to relay terminals will be turned ON/OFF by the TTL. Contact closed if TTL = High Contact opened if TTL = Low TTL +5V Vs Figure 9.3 Driving circuit of an electromagnetic relay 7

8 Solid State Relays/Switches Solid-state relays has no mechanical parts and made of semiconductor materials It combines the isolation, driving, and contact closure functions into a single package It is commonly use to control ac loads Relay closed if input = High Relay opened if input = Low Input Control + SSR T1 T2 a.c. power supply Figure 9.4 Driving a solid state relay 8

9 Light-Emitting Diode (LED) Light-emitting diodes (LEDs) can be turned on when a current passes through it. Figure 9.5 Shows a typical TTL circuit driving a LED The 330Ω resistor is used to limit the amount of current to pass through the LED to prevent it burning off. The TTL output is LOW, the LED will ON The TTL output is HIGH, the LED will OFF +5V 330Ω TTL Figure 9.5 9

10 Control of LEDs +5V EA V CC Reset P1.7 P1.6 8 LEDs are connected to Port 1 and linked to 5V supply 8051 P1.5 P1.4 The LEDs can directly be turned ON/OFF by the 8051 XTAL1 XTAL2 V SS P1.3 P1.2 P1.1 P1.0 Figure 9.6 Under this connection, the LEDs will be OFF when port bit is at logic 1 ON when port bit is at logic 0 10

11 Example 9.1 : Control the 8 LEDs ON/OFF at the same time All LEDs ON All LEDs OFF 11

12 Program Listing for Example 9.1 Start Set A = 00 Move the content of A to P1 Delay for 0.1s Invert the content of A ORG 0000H CLR A LOOP: MOV P1, A CPL A ACALL DELAY AJMP LOOP DELAY: MOV R6, #250 DL1: MOV R7, #200 DL2: DJNZ R7, DL2 DJNZ R6, DL1 RET END Assume 12MHz clock, determine the delay time. 12

13 Example 9.2 : Glowing a LED in rotating sequence ORG 0000H START: MOV R1, #07H MOV A, # B LEFT: MOV P1, A ACALL DELAY RL A DJNZ R1, LEFT ; MOV R1, #07H MOV A, # B RIGHT: MOV P1, A ACALL DELAY RR A DJNZ R1, RIGHT AJMP START ; DELAY:. 13

14 Example 9.3: Turning LEDs ON/OFF in a preset sequence by using a Look-up Table 14

15 Program Listing of Example 9.3 ORG 0000H START: MOV R0, #OK DATA+1 MOV DPTR, #DATA MOV R1, #00H LOOP: MOV A, R1 MOVC MOV P1, A ACALL DELAY INC R1 DJNZ R0, LOOP AJMP START ; DELAY: MOV R5, #2 DL1: MOV R6, #250 DL2: MOV R7, #200 DL3: DJNZ R7, DL3 DJNZ R6, DL2 DJNZ R5, DL1 RET ; DATA: DB B DB B DB B DB B DB B DB B DB B DB B ; DB B DB B DB B DB B DB B DB B DB B DB B ; DB B DB B DB B OK: DB B END 15

16 Exercise: Write a 8051 program, using a look-up table, to light-up the LEDs in the sequence as shown below 16

17 Simple I/O applications +5V EA V CC Reset XTAL P1.7 P1.6 P1.5 P1.4 P1.3 P1.2 P1.1 P1.0 Figure 9.7 XTAL2 P3.7 P3.6 P3.5 P3.4 SW1 SW2 SW3 SW4 V SS 17

18 Example 9.4: Refer to the 8051 circuit in figure 9.5, write a 8051 program to light-up the LEDs in the pattern as shown below when the respect switch is closed. When SW1 Closed When SW2 Closed When SW3 Closed When SW4 Closed Priority: SW1 SW2 SW3 SW4 18

19 Flow Chart of Example Start SW1 closed? Y SW1 Handler 1 Initialization 2 N SW2 closed? Y SW2 Handler Set P3 as input port N SW3closed? Y SW3 Handler Read SW1 SW4 status N SW4 closed? Y SW4 Handler 1 19

20 Program Listing of Example 9.4 ORG 0000H MOV R1, # B MOV R2, # B MOV R3, # B MOV R4, # B ; TEST: ORL P3, #0FFH JNB P3.7, CASE1 JNB P3.6, CASE2 JNB P3.5, CASE3 JNB P3.4, CASE4 AJMP TEST ; CASE1: MOV A, R1 MOV P1, A ACALL DELAY XRL A, # B MOV P1, A AJMP TEST ; CASE2 MOV A, R2 MOV P1, A ACALL DELAY XRL A, # B MOV P1, A AJMP TEST ; CASE3 MOV A, R3 MOV P1, A ACALL DELAY XRL A, # B MOV P1, A AJMP TEST ; CASE4 MOV A, R4 MOV P1, A ACALL DELAY XRL A, # B MOV P1, A AJMP TEST ; DELAY:.. END 20

21 7-Segment LED Numeric Display A single-character display panel Contains 7 LED segments arranged as an 8 Two configurations: common-anode and common-cathode a f e g d b c Dp Segment Pattern 21

22 7-Segment LED Numeric Display Common-anode configuration Common a b c d e f g Dp Common-cathode configuration Common a b c d e f g Dp 22

23 7-Segment LED Numeric Display Segment displays are driven by connecting each segment to a port bit, or they can be driven by decoder/driver IC Output Port bit Display segment Dp g f e d c b a Normally the LED should be connected to the power via resistors to protect them from burning When using common-cathode configuration, a segment will be lit only if the lead of the segment connected with a High voltage and the common cathode lead with Low voltage 23

24 7-Segment LED Numeric Display EEE3410 Microcontroller Applications XTAL1 XTAL P2.0 P2.1 P2.2 P2.3 P2.4 P2.5 P2.6 P2.7 Vcc a b a c d f b g e f e c g Dp d Dp.. Figure 9.8 Use R3 as counter, write a 8051 assembly language program using look-up table method, to display the value in R3 to a 7-segment display 24

25 Program Listing ORG 0000H MOV R3, #00H LOOP: MOV DPTR, #TABLE MOV A, R3 MOVC ; ; Display numbers on 7-segment display MOV P1, A ACALL DELAY ; ; Increase R3 by 1 and loop back MOV A, R3 ADD A, #1 DA A ANL A, #0FH MOV R3, A AJMP LOOP ; DELAY:.. TABLE: DB B ; 0 DB B ; 1 DB B ; 2 DB B ; 3 DB B ; 4 DB B ; 5 DB B ; 6 DB B ; 7 DB B ; 8 DB B ; 9 ; END 25

26 Dot-matrix LED Display Consists of a number of LED arranged in the form of a matrix e.g. 35 LED in a 5 columns x 7 rows matrix, or 64 LED in a 8 x 8 matrix a b c d e f g To display a digit/character, use the method of scanning i.e. scan a column at a time. If the scanning is fast enough, it appears that the digit/character is displayed (due to illusion of our eyes) 26

27 Dot-matrix LED Display Internal circuitry of a 5 x 7 dot matrix display is shown on the right Voltage should be supplied to terminals C and 1 to light up the LED indicated in this picture a b c d e f g

28 Dot-matrix LED Display EA Reset 8051 XTAL1 XTAL2 Vcc V SS P3.0 P3.1 P3.2 P3.3 P3.4 P3.5 P3.6 P1.0 P1.1 P1.2 P1.3 P a b c d e f g 28

29 Dot-matrix LED Display EEE3410 Microcontroller Applications Example: Displaying the character E on the dot-matrix. a b c d e fg a b c d e fg a b c d e fg a b c d e fg isplaying the character E on the 5x7dot-matrix Step 1: signals on pins pins pins gfedcba Step 2: signals on pins pins pins gfedcba Step 3: signals on pins pins pins gfedcba a b c d e fg a b c d e fg Step 4: signals on pins pins pins gfedcba

30 Code Words and Displays of 0 to B B B B B B B B B B B B B B B B B B B B B B B B B 30

31 Code Words and Displays of 5 to B B B B B B B B B B B B B B B B B B B B B B B B B 31

32 Program Listing character display on 5x7 Dot-matrix display (1/2) ORG 0000H START: MOV DPTR, #TABLE ; point to the starting add of 1 st char MOV R3, #10 ; display 10 characters LOOP: MOV R2, #100 ; scan 100 times for each character SCAN: ACALL SACN1 ; 10ms x 100 = 1000ms DJNZ R2, SCAN INC DPTR ; increase DPTR by 5 to INC DPTR ; point to the starting address of INC DPTR ; the next character INC DPTR INC DPTR DJNZ R3, LOOP ; loop back to display 10 char AJMP START ; ====================== ; == Scan Subroutine == ; ====================== SCAN1 MOV R1, #00H ; R1 points to the starting add of a char MOV R5, # B ; start from the leftmost column MOV R4, #05 ; there are 5 columns LOOP1 MOV A, R1 ; get the code at add R1+DPTR MOVC MOV P3, A ; send the code to the dot-matrix display MOV P1, R5 ; turn-on a particular transistor 32

33 Program Listing character display on 5x7 Dot-matrix display (2/2) MOV R6, #5 ; delay for 2ms DL1: MOV R7, #200 DL2: DJNZ R7, DL2 DJNZ R6, DL1 ORL P1, # B ; turn-off display MOV A, R5 ; RL A ; move to next column MOV R5, A ; totally there are 5 columns INC R1 ; DJNZ R4, LOOP1 ; RET ; return the main program ; ============================ ; == Character Table == ; ============================ TABLE: DB B ; codes for 0 DB B DB B DB B DB B DB B ; code for 1 : ; codes for 2 to 9 : ; END 33

34 Department of Electrical Engineering END of Lecture 9 Simple I/O Interfacing Week 10 1

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