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Chapter 4

Chapter 4. Programming and Problem Solving. Flowchart A graphical representation of processes (tasks) to be performed and the sequence to be followed in solving computational problem. Flowcharting. Example 4.1 (1 of 2).

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Chapter 4

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  1. Chapter 4 Programming and Problem Solving

  2. Flowchart A graphical representation of processes (tasks) to be performed and the sequence to be followed in solving computational problem Flowcharting

  3. Example 4.1 (1 of 2) • Write instructions to load two bytes (37H and 92H) in data registers REG0 and REG1. Add the bytes and store the sum in REG2. • Steps • Load the two bytes in data registers REG0 and REG1. • Add the bytes. • Save the sum in data register REG2.

  4. Example 4.1(2 of 2) Start ORG 0x20 REG0 EQU 0x00 REG1 EQU 0x01 REG2 EQU 0x02 MOVLW 0x37 MOVWF REG0,0 MOVLW 0x92 MOVWF REG1,0 ADDWF REG0,0 MOVWF REG2, 0 SLEEP Process Change the program: if the sum is larger than 50H then the result should be in REG3 AND REG2=0; OTHERWISE, the result should be in REG2 AND REG3=0;

  5. What is wrong with this? ORG 0x20 REG0 EQU 0x00 REG1 EQU 0x01 REG2 EQU 0x02 REG3 EQU 0x03 COMPREG EQU 0x10 CONST EQU 0x50 MOVLW CONST MOVWF COMPREG,0 MOVLW 0x37 MOVWF REG0,0 MOVLW 0x92 MOVWF REG1,0 ADDWF REG0,0 ;the result is in W CPFSLT COMPREG,0 BRA WR_REG3 BRA WR_REG2 WR_REG3: MOVWF REG3, 0 BRA DONE_PROG WR_REG2: MOVWF REG2, 0 DONE_PROG: SLEEP

  6. Steps in Writing and Executing Assembly Language Program • Analyze the problem. • Draw a flowchart. • Convert the flowchart in mnemonics. • Look up Hex code and assign memory addresses. • Enter the Hex code into memory of a lab training board. • Execute the program. • Debug the program if necessary.

  7. Illustrative Program: Addition With Carry Check • Write instructions to load two bytes, Byte1 (F2H) and Byte2 (32H), in data registers REG0 and REG1 respectively and add the bytes. • If the sum generates a carry, clear the data register REG2; otherwise, save the sum in REG2.

  8. Illustrative Program: Addition With Carry Check (1 of 2) Write instructions to load two bytes, Byte1 (F2H) and Byte2 (32H), in data registers REG0 and REG1 respectively and add the bytes. If the sum generates a carry, clear the data register REG2; otherwise, save the sum in REG2.

  9. Integrated Development Environment (IDE) • Steps in using IDE • Editing – generating the source code • Assembling – Converting mnemonics into hex and binary; generates the object file • Linking – uses the object file and generates the binary code • Downloading – transfers the binary code (instructions) to the memory of the target device • Executing – perform the tasks specified by instruction codes • Simulation – Execute the program on PC (also called the simulator) • Debugging – Going through the program step-by-step to find logical problems in the instruction set

  10. Writing a Program Using an Assembler • The assembly language program includes: • Program in mnemonics • Assembler directives • Comments

  11. Assembly Language Format (1 of 2) • Typical statement of an assembly language source code has four fields: • Label • Opcode (operation code) • Operand (data, register, or memory address to be operated on) • Comment

  12. Assembly Language Format (2 of 2) • Format example Label Opcode Operand Comment START: MOVLW 0xF2 ;Load F2H in W ↑↑↑↑ Space Space Space Semicolon Or Colon

  13. Assembler Directives • ORG Origin • END End of assembly • EQU Equate • SET Defines an assembler variable • #INCLUDE Include resources from available library • RADIX Number format • DB Define byte • DW Define word • CBLOCK Define a block of constants • ENDC End of block of constants • RES Reserve memory

  14. View Registers and Source Program in MPLAB Simulator Data bytes Define labels and const Starting memory address Label

  15. Format of Radixes • Hexadecimal • 0x0F • H`4F` • 4F • 4FH • Decimal • D`200` • Binary • B`1001` • ASCII • `This stuff are interesting!`

  16. Using MPLAB IDE to Write, Assemble, and Build Project (1 of 6) • Write source code using MPLAB editor. • Create a new project. • Select language tool suite. • Name your project. • Add files to assemble. • Build the project.

  17. Using MPLAB IDE (2 of 6) • To create a new project • Step 1: Open MPLAB IDE Select Project  Project Wizard  Select Device PIC18F452 Next

  18. Using MPLAB IDE (3 of 6) • Step 2: Select a Language Toolsuite: Microchip MPASM Toolsuite Next

  19. Using MPLAB IDE (4 of 6) • Step 3. Name Your Project: Illust4-4 Addition with Carry Check Browse  MyProj\Ch04  Next

  20. Using MPLAB IDE (5 of 6) • Step 4: Add  Add Source Files  Next

  21. Using MPLAB IDE (6 of 6) • Summary  Finish

  22. Project Window

  23. List of Files Generated by MPLAB Assembler

  24. Understanding the List File • List file generated primarily for documentation • Includes seven columns • Memory addresses where binary code is stored • Hex code • Line numbers • Contents of source file • Labels • Opcode • Operands • Comments

  25. Executing a Program Using Simulator • Steps in setting up MPLAB simulator • Select Debugger  Select tool MPLABSIM • Select Debugger  Settings  Change frequency if necessary • Select View  Watch  Add registers to observe

  26. View Registers and Source Program in MPLAB Simulator

  27. View Registers, Source Program, and Program Memory in MPLAB Simulator

  28. Debugging a Program • Single-step technique • Enables user to execute one instruction at a time and observe registers for expected results • Breakpoint technique • Enables user to execute a group of instructions at a time and observe registers for expected results • Tracing code • MPLAB can track execution of each instruction and display data which can be examined for errors

  29. Single-Step Technique

  30. Breakpoint Technique

  31. Tracing Code

  32. Assembler Directive • Pseudo-code instructions • Define constants, labels, where to assemble a program, reserves memory for data • Directives do not translate to machine language  do not require memory assignment (come for free!) • Example BYTE EQU 0x02 • Label BYTE is being equated to value 2Hex • Example ORG 20H • Assemble the program starting at location 20H

  33. Number Representation

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