CPEG300 Embedded System Design. Lecture Interface with Peripheral Devices

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1 CPEG300 Embedded System Design Lecture Interface with Peripheral Devices Hamad Bin Khalifa University, Spring 208

2 Typical Devices for an Electronics System Power generation PWM control Input devices Keyboard Sensors, A/Ds Output devices LED Display o 7-segment, LCD Speakers Actuators: Motor Servo motor Hamad Bin Khalifa University, 208 2

3 Interface with A/D (/4) Real world data is analog Temperature Pressure Intensity of light Acceleration Force Flow Magnitude Time Continuous-time signal Discrete-time, quantized data Sensors/Transducers measure the real world quantity and convert it into proportional electrical signals. Microcontrollers process digital data Analog to Digital Converters convert analog data into equivalent digital data. Hamad Bin Khalifa University, 208 3

4 Interface with A/D (2/4) A/D Terminologies: Resolution (e.g., 8, 0, 2, 6 and 24 bits) o Higher resolution provides closer estimation of original signal Step size o the smallest change that can be detected by the ADC Conversion Time o Time it takes to convert analog input to digital output Sensor Analog Signal ADC 805 CS WR INTR RD 8-bit Digital output Hamad Bin Khalifa University, 208 4

5 Interface with A/D (3/4) A/D Types: ADC bit parallel SAR ADC D0 D7 o 8-bit parallel binary data output Vin(+) and Vin(-) o Differential analog input voltage CS* o ADC chip select WR* o L-to-H transition to start conversion INTR* o End of Conversion RD* o Read data from internal register Hamad Bin Khalifa University, 208 5

6 Interface with A/D (4/4) Interface program: RD BIT P3.6 WR BIT P3.5 INTR BIT P3.4 CS BIT P3.7 MYDATA EQU P MOV P, #0FF H ; i/p port CLR CS ; CS = 0 CLR WR ; WR = 0 SETB WR ; L to H transition starts conversion here: JB INTR, here ; wait for end of conversion CLR RD ; enable RD MOV A, MYDATA ; read data from ADC ACALL conversion ; convert binary data to ASCII Hamad Bin Khalifa University, 208 6

7 Interface with Keyboard (/3) Matrix keyboard To processor interrupt input 4-bit input Port +5 V 4-bit output Port Hamad Bin Khalifa University, 208 7

8 Interface with Keyboard (2/3) Scanning process: Logic 0000 is sent through output port 0 on the row line if any key is pressed o Interrupt (logic 0) sent to microcontroller o ISR executes a scanning program to identify the key scanning program: Logic 0 is sent through output port o The logic level on one of the row line is 0 if any key is pressed in st column. Logic 0 is sent through output port. o The logic level on one of the row line is 0 if any key is pressed in 2nd column. To processor interrupt input 4-bit input Port +5 V 4-bit output Port Hamad Bin Khalifa University, 208 8

9 Interface with Keyboard (3/3) Interfacing a 4 x 4 keypad: P2.4 to P2.7 Input P2.0 to P2.3 Output Scan pattern output through 4-bit output port Scan pattern read through 4- bit input port I/P X 5 H H H H MOV R0, #4 ;4 scan patterns MOV A,#F7H ;scan pattern again: MOV R7, A ;save scan pattern MOV P2, A ; out scan pattern MOV A, P2 ; read rows ANL A, #0F0H ;mask off columns CJNE A, #0F0, keyht ;check key pressed MOV A, R7; read scan pattern RR A ;next scan pattern DJNZ R0, again ;repeat scan pattern keyht: MOV R7, A MOV A, #4 CLR C SUBB A, R0 MOV R6, A MOV A, R7 NEXT: RLC A JNC done INC R6 INC R6 INC R6 INC R6 SJMP NEXT done: MOV A, R6 ;save row number ;save ;restore scan code ;add 4 for different row O/P Hamad Bin Khalifa University, 208 9

to write to the register; High to read from the Read/write register 6 Sends data to data pins when a high to low pulse is Enable given 7-3 7-bit data

10 Interface with LCD (/4) Liquid crystal display Pin No Function Name Ground (0V) Ground 2 Supply voltage; 5V (4.7V 5.3V) Vcc 3 Contrast adjustment; through a variable resistor V EE 4 Selects command register Register when low; and data register Select when high 5 Low to write to the register; High to read from the Read/write register 6 Sends data to data pins when a high to low pulse is Enable given bit data pins D0-D6 4 Data Bit 7/Busy Flag D7 5 Backlight VCC (5V) Led+ 6 Backlight Ground (0V) Led- 6 x 2 means it can display 6 characters per line; 2 lines available Hamad Bin Khalifa University, 208 0

11 Interface with LCD (2/4) Timing diagram A high-to-low pulse must be applied to E pin to latch data in. Setup and hold time varies for different devices, check datasheet before programming. The next data value can be written after checking the busy flag D7 = Busy flag (D7 is 0 if data processing finished) Hamad Bin Khalifa University, 208

12 Interface with LCD (3/4) Steps for Sending Command/Data: step: Send the command/character to LCD. step2: Select the Data Register by making RS low/high. step3: Select Write operation making RW low. step4: Send a High-to-Low pulse on Enable PIN with some delay for successful writing. void LCD_CmdWrite( char cmd) { LcdDataBus=cmd; // Send the command to LCD LCD_RS=0; // Select Command Register by pulling RS LOW LCD_RW=0; // Select the Write Operation by pulling RW LOW LCD_EN=; // Send a High-to-Low Pusle at Enable Pin delay_us(0); LCD_EN=0; delay_us(000); } void LCD_DataWrite( char dat) { LcdDataBus=dat; // Send the data to LCD LCD_RS=; // Select the Data Register by pulling RS HIGH LCD_RW=0; // Select the Write Operation by pulling RW LOW LCD_EN=; // Send a High-to-Low Pusle at Enable Pin delay_us(0); LCD_EN=0; delay_us(000); } Hamad Bin Khalifa University, 208 2

13 Interface with LCD (4/4) Displaying NO on LCD MAIN: MOV A, #38H ; LCD 2 lines 5x7 matrix ACALL Comwrt ; write command ACALL Delay ; wait for LCD MOV A, #0EH ; Display on, Cursor on ACALL Comwrt ; write command ACALL Delay ; wait for LCD MOV A, #0 ; clear LCD ACALL Comwrt ; write command ACALL Delay ; wait for LCD MOV A, #06 ; shift cursor right ACALL Comwrt ; write command ACALL Delay ; wait for LCD MOV A, #84H ; cursor at line, pos. 4 ACALL Comwrt ; write command ACALL Delay ; wait for LCD MOV A, # N ; display N ACALL Datwrt ; write data ACALL Delay ; wait for LCD MOV A, # O ACALL Datwrt ACALL Delay Delay: MOV R3, #50 Here2: MOV R4, #255 Here: DJNZ R4, Here DJNZ R3, Here2 RET ; display O ; write data ; wait for LCD COMWRT:MOV P, A; write to Port CLR P3.5 ; RS = 0 CLR P3.4 ; R/W* = 0 SETB P3.3 ; E = ACALL Delay CLR P3.3 ; E = 0 RET DATWRT:MOV P, A; write to Port SETB P3.5 ; RS = CLR P3.4 ; R/W* = 0 SETB P3.3 ; E = ACALL Delay CLR P3.3 ; E = 0 RET Hamad Bin Khalifa University, 208 3

Interface with Step Motor (/3) Stepper Motors used for position control Printers, Robots, Scanning, Tracking Stepper Motors can have small very precise steps Permanent Magnetic

14 Interface with Step Motor (/3) Stepper Motors used for position control Printers, Robots, Scanning, Tracking Stepper Motors can have small very precise steps Permanent Magnetic Rotor surrounded by a Stator C S N A S N A B COM B N S D C D COM 4 step stepping sequence, 90 0 step (Wave Drive) Step A D B C Hamad Bin Khalifa University, 208 4

15 Interface with Step Motor (2/3) 8 step stepping sequence, 45 0 step (Half-Step) Step A D B C MAIN: MOV motor, #08H ACALL delay MOV motor, #0CH ACALL delay MOV motor, #04H ACALL delay MOV motor, #06H ACALL delay Driving circuit MOV motor, #02H ACALL delay MOV motor, #03H ACALL delay MOV motor, #0H ACALL delay MOV motor, #09H ACALL delay SJMP MAIN Hamad Bin Khalifa University, 208 5

16 Interface with Step Motor (3/3) Microcontroller generates step patterns which drives stepper motor Speed Control is determined by delay between each step Direction: o Rotation direction determined by sequence of step patterns o Rotation direction selected by a switch ORG 0000H Main: SETB P2.7 ; input direction MOV A, #66H ; starting pattern 0000 MOV P, A ; send to motor Turn: JNB P2.7 CW ; check switch RR A ; rotate right ACALL Delay MOV P, A ; send to motor SJMP Turn CW: RL A ; rotate left ACALL Delay MOV P, A ; send to motor SJMP Turn Hamad Bin Khalifa University, 208 6

8051 Interfacing and Applications Microcontroller

8051 Interfacing and Applications Objectives: At the end of this chapter, we will be able to: List the different devices that can be interfaced with 8051 Understand the working principle. Develop the following