Embedded system (Chapter 2) part 2


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Embedded system (Chapter 2) part 2

  2. 2. OUTCOMES  Know PIC Assembly Language fundamental
  3. 3. Overview  PIC - "Peripheral Interface Controller”  How to use PIC microcontroller?  Hardware  Software - programming  Programming language  Machine language – machine code  Assembly language  High level language  C, C++, Basic Low level language
  4. 4. Introduction  Assembly language is programming language use to write programs using instructions that are the symbolic code called mnemonic.  Assembly language programs must to be translated into machine code by a program called assembler.
  5. 5.  To program in assembly language, the programmer must know all the registers of the CPU and the size of each, as well as other details.
  6. 6. Assembling and linking process  First use a text editor to type program in assembly language. In the case of PIC microcontrollers, we use the MPLAB IDE.  The “asm” source file is fed into PIC assembler. The assembler converts the instructions into machine code.  The third step is called linking. The link program takes one or more object files and produces a hex file, a list file, a map file, an intermediate abject file and a debug file.  After a successful link, the hex file is ready to be burned into PIC’s program ROM and is downloaded into PIC trainers.
  7. 7. Sample o a PIC Assembly Source Code (asm file)
  8. 8. Assembler Directives  While instruction tell the CPU what to do, directives (also called pseudo-instructions) give direction to the assembler.  Assembler directives are instruction used to tell the CPU what to do.  Examples of assembler directive : EQU – equate (use to define value or a fixed address) ORG – origin (use to indicate the beginning of the address for code or data) END – indicate the end of the source (asm) file.
  9. 9. Review Questions 1. What is the purpose of pseudo-instructions? 2. _____________ are translated by the assembler into machine code, whereas _____________are not. 3. True or false. Assembly language is a high- level language. 4. Pseudo- instruction are also called __________. 5. True or false. Assembler directives are not used by the CPU itself. /they are simply guide to the assembler. 6. Which one the following is an assembler directive? a) MOVLW 25H b) ADDLW 12 c) ORG 200H d) GOTO HERE
  10. 10. Data Format Representation  The following are data type and data format using for PIC microcontrollers. Data Type Data Format Hexadecimal 99H 0X99 h’99’ 99 Decimal D’12’ Binary B’10011001’ ASCII A’2’
  11. 11. PIC18F instruction set.  PIC18F2455/2550/4455/4550 devices incorporate the standard set of 75 core instructions.
  12. 12. PIC18F instruction set.
  13. 13. PIC18F instruction set (cont.)
  14. 14. PIC18F instruction set (cont.)
  15. 15. MOVLW Instruction  MOVLW Instruction moves 8-bit data into WREG register. It has the following format: MOVLW K ;move literal value K into WREG  Example: Load the WREG register with value 25H. MOVLW 25H ;move value 25H into WREG (WREG = 25H) Operation: k → W
  16. 16. MOVWF Instruction  The MOVWF instruction tells the CPU to move (in reality, copy) the source register of WREG to a destination register in file register (F).  Example: Load value 66H into Port B, C and D. MOVLW 66H ;move the value 66H to WREG (WREG = 66H) MOVWF PORTB ; move the value in WREG to PORTB (PORTB = 66H) MOVWF PORTC ;PORTC = 66H MOVWF PORTD ;PORTD = 66H MOVWF Move W to f Operation: (W) → f
  17. 17. Example  Write assembly instruction to make the I/O port as below : a) RB4 and RB5 as input b) PORTC as output Solution: a) MOVLW B’00110000’ MOVWF TRISB b) MOVLW B’00110000’ MOVWF TRISB
  18. 18. Arithmetic Instruction  Instructions for performing 8-bit addition, subtraction and multiplication operation.
  19. 19. Addition  These ADD instructions are design to perform 8- bit addition.  The execution result of the ADD instruction will affect all flag bits of the STATUS register. Operation: (W) + k → W
  20. 20. Addition (cont..) Example Write a program that add the hexadecimal numbers 0x20 and 0x30. Store the sum in data register at 0x50. ORG 0X00 MOVLW 0X20 ADDLW 0X30 MOVWF 0X50,A END
  21. 21. Example
  22. 22. Subtraction • PIC18 microcontroller has two SUBTRACT instructions. Subtract instruction will also affect all the flag of STATUS register. SUBLW Subtract W from Literal Operation: k – (W) → W SUBWF Subtract W from f Operation: (f) – (W) → dest
  23. 23. Subtraction Example  Write a program to subtract 5 from 40H. Identify the flag bit in status register. Solution: #include <pic18f4550> ORG 0X00 MOVLW D’5’ SUBLW 0X40 END
  24. 24. Logic Instruction  The logical instruction allow user to perform AND, OR, exclusive-OR and complementing on 8-bit numbers.
  25. 25. Example Example : Write assembly statement for the operation 0XFF || 0X55 MOVLW 0XFF ;move the value 0xFFin to WREG IORLW 0X55 ;OR the value in WREG with value 0x55
  26. 26. Review Questions
  27. 27. Bit manipulation  The bit operations set, clear and toggle test only a single bit. The bit oriented instructions available to PIC family are BCF, BSF, BTFSC, BTFSS and BTG. BCF Bit Clear f Operation: 0 → f<b> BSF Bit Set f Operation: 1 → f<b>
  28. 28. Bit manipulation Example: Write an assembly statement to make RB4 as input an RC7 as output using bit addressable. Solution: BSF TRISB,4 ; set RB4 as input BCF TRISC,7 ; make RC7 as output
  29. 29. Rotate Instruction  PIC 18 families has four rotate instructions. Figure 2. Illustrates this four rotate instructions. RLCF Rotate Left f through Carry RLNCF Rotate Left f (No Carry) RRCF Rotate Right f through Carry RRNCF Rotate Right f (No Carry)
  30. 30. Rotate Example: RLCF
  31. 31. Data serialization  One of the most widely used applications of the rotate instructions. Data serialization is a process of sending a byte of data, one bit at a time through a single pin of microcontroller.  The characteristic of data serialization are:  Using the serial port.  Using a programming technique to transfer data one bit at a time and control the sequence of data and spaces between them.
  32. 32. Data serialization Example Write a program to bring in a byte of data serially via pin RC7 and save it in file register location 0x21. The byte comes in with the LSB first. Solution: RCNT EQU 0x20 MYREG EQU 0x21 BSF TRISC,7 MOVLW 0x8 MOVWF RCNT AGAIN BTFSC PORTC 7 BSF STATUS,C BTFSS PORTC,7 BCF STATUS,C RRCF MYREG,F DECF RCNT F BNZ AGAIN
  33. 33. Review Questions
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