Microprocessors and Microcontrollers. Lab #0 Getting Started with MPLAB-X IDE

Transcription

1 EE 3954 Microprocessors and Microcontrollers Lab #0 Getting Started with MPLAB-X IDE Background: Some or all of the laboratory exercises performed throughout this course will involve writing assembly language programs that will eventually be uploaded and run on the PIC 16F877 microcontroller development boards in the lab. The final goal is to create a runtime program that fulfills the design specifications for each lab exercise. An ideal scenario would be to write the program and have it work perfectly the first time. Reality suggests that this is rarely true. The actual design cycle is: write the program, compile/assemble the program, test the program, debug the program, and repeat until a successful run-time program is achieved. MPLAB-X is an Integrated Development Environment (IDE) that contains tools to implement various stages of the design cycle. In particular, it contains an editor, a compiler/cross-assembler, a simulator, a debugger, and an interface to the ICD3 programmer and development board. Purpose: The purpose of this experiment is to familiarize you with the tools available to: Preparation: a) write PIC microcontroller assembly language programs, b) simulate your programs, c) program PIC microcontroller devices, d) in-circuit debug your programs. In order to prepare you sufficiently for this lab read the following: 1) Section 9.1 (I/O Ports) in the Reference Manual 2) Students Guide to Flow Charts Both documents were provided to you via attachments or on BlackBoard. Task 0: Using the Students Guide to Flow Charts, and the instruction table in the Reference Manual- Section 29, study the flowchart at the end of this document. For those enthusiasts that want to use the MPLAB-X IDE software before performing the lab exercise in lab, and who have access to a computer, MPLAB X (the software that we use in the labs) can be obtained from the Microchip home website 1

2 Note: For assistance throughout this exercise refer to MPLAB-X IDE help: Help / Help Contents, the lab s teaching assistant, or the instructor. More information and useful tools can be found by reading the MPLAB-X IDE HELP and MPASM Assembler in the help as well online manuals. 2

3 1. Writing, Assembling, Compiling Programs Using MPLAB-X The first step is to start a new project. Follow the given instructions. 1. Open MPLAB-X 2. Select Menu / File / New Project 3. Select Microchip Embedded and Standalone Project and click Next 4. Select Family: Mid-Range 8-bit MCUs (PIC 12/16/MCP) and Device: PIC16F877 and click Next 5. Select the Simulator and click Next 6. Select the MPLAB assembler mpasm (v5.50 )and click Next 7. Create a new Project Name (make sure to pick a name that makes sense like lab00prj ) and select a Project Location (preferably your USB memory stick) and click Finish. 8. If you have already typed the assembly code (or downloaded the file), you must add it here. In the Project window, Right-click the Source Files then Add Existing Item and select the lab0code.asm file from the location where you have it stored. Once the Source file is added, double-left click on its name to open it in the editor. If you are going to type in a new assembly program follow these steps: (you shouldn t have to do this for this exercise, you already have the lab0code.asm file) 1. Open a new file using Menu / File / New File or by clicking on 2. Select the Project that you just created, and 3. Select the File Type as Assembler and Assembly File.asm and click Next 4. Select a File Name and click Finish; your file has now been added to the project automatically. 5. Create your assembly program using the editor. Save your files by selecting Menu / File / Save or by clicking on NOTE: If you close MPLAB and you want to reopen the project you were working on select: Menu / File / Open Project, go to your directory and select your project, if it did not already open. Next, you want to assemble and compile your program: 1. Select Menu / Run / Build Project or by clicking on 2. The program should compile and at that point the Output window at the bottom of the Integrated Development Environment (IDE) should show you the progress of the assembling stage. If the program compiled successfully, the message BUILD SUCCESSFUL will be indicated. The program will then be loaded into the target program memory. Wait until the Loading Completed message appears in the output window before continuing. If the program failed to compile successfully, this window will show the lines that 3

4 had errors. You will have to go back to the editor window and make corrections and recompile the program. You can observe the generated machine code: 1. Select Menu / Window / Output / Disassembly Listing File to view the compiled source program. 2. Select Menu / Window / PIC Memory Views / Program Memory to view the contents of program memory. Task 1: Write down what the main difference is between the Disassembly Listing File windows and the Program Memory. When you have completed this task, close the Disassembly Listing File and Program Memory windows. 2. Simulating Programs Using the Debugging Tool: Before uploading your assembled program to the microcontroller laboratory boards, it may be helpful to verify that your program works. This can be done by simulating its function in the MPLAB X IDE environment. The simulator device was selected when the project was created in Part 1. The only way a simulator is useful is if you can observe various program and data memory entries such as the Special Function Registers and the General Purpose Registers. The contents of the various memories/registers can be examined by opening specific windows to observe them. These windows can be found under Menu / Window / PIC Memory Views. Selecting Program Memory lets you inspect the contents of the Program Memory; Selecting File Registers lets you inspect the contents of all Data Memory; Selecting SFRs lets you inspect the special function registers only (they will be given by name). Selecting Menu / Window / Debugging / Watches or Variables enables you to select both SFRs and the variables (symbols) you defined. Task2: Task 3: Select Menu / Window / Debugging /Watches to open a watch window. To add a Watch register or variable, move the cursor over the register or label in the source file and right-click on it, a menu will appear that allows you to add this as a New Watch item. Enter the variables TRISD, TRISB, PORTB, PORTD, STATUS and WREG (select new watch and type this name in). Right click on the Value column and select Binary as the viewed format. When run on the development boards in the lab, the user will press the RB0 button to allow each segment of the display (PORTD) to turn on in succession. When run in the simulator, there is no RB0 button, so this action must be simulated. This is done by defining a Stimulus to the simulator. To create a stimulus select: Menu / Window / Simulator/ Stimulus. A Stimulus 4

5 window will open. Select the Asynchronous tab. Position the cursor in the first row, under the Pin column and click to highlight the cell. Scroll down to select RB0 from the list. Under Action, select Set High. Then select the icon for Add a Row. In the new row, define the Pin as RB0, and the Action as Pulse Low, the Width as 20, and Units as cycles. 1. Build the project by selecting Menu / Debug / Debug Project. 2. At this point a small toolbar will appear telling you that the simulator is up and running in debug mode: The simulator buttons have the following function: Run your program in simulation mode (shortcut key: F5) Halt/Pause the simulation (shortcut key: F5) Step through your program and steps into a subroutine if one is encountered (shortcut key: F7) Step through your program and steps over a subroutine if one is encountered (shortcut key: F8) Run to the line of code where you have put the cursor (shortcut key: F4) Reset your program Manage program breakpoints 3. When the debugger is launched, the program may or may not start running. You can tell if it is running by observing the progress bar at the bottom of the MPLAB X window. If the program is running, stop it by clicking on the Pause icon., then Reset to stop it and allow it to start from the first instruction. A highlighted line in the assembly code will indicate the position of the first instruction to be executed when the program runs. Task 4: Step through your program using the simulator. Observe the variables in the Watch window and document what happens to the various registers as your program executes each instruction. Verify the program s operation follows the flow chart by using the simulator. Do this for RB0=set high, and when RB0 pulses low for 20 cycles (use the mouse cursor to Fire the Stimulus event). Observe Port B, bit 0 and all bits of Port D while stepping through the program. When finished, close the debugger by selecting Finish Debugger Session. 5

6 3. PROGRAMMING PIC MICRO-CONTROLLERS USING MPLAB-X Now, you have simulated the program, it is time to download it to the Laboratory development board, observe its behavior, and compare the behavior to the simulated behavior. First, MPLAB-X must be connected to the programming device. The programming device used in this lab is the ICD-3 (In-Circuit Debugger). Changing from Simulator device to ICD3 device: 1. Apply power to the PIC development board. 2. In the left window right-click on your project, click on Properties and select ICD3 in the middle window under the Hardware Tools (make sure that the Simulator is stopped), then click OK. 3. If error messages occur in the Output window, contact the TA or the instructor. Now MPLAB-X is connected to the laboratory board, you can program the device: 1. Program the device by selecting Make and Program Device from the Dropdown button. 2. A voltage caution prompt will appear asking you to be sure you are connecting to a 5V device. Press OK. In lab you will always be using a 5V PIC. 3. The Output window will show a message Programming/Verify complete if the programming stage was successful 4. DEBUGGING PROGRAMS USING MPLAB-X In order to debug your program, you must start the ICD-3 following the instructions in the previous section and: 1. Program the device by selecting Program Device for Debugging from the drop-down button. 2. A voltage caution prompt will appear asking you to be sure you are connecting to a 5V device. Press OK. In lab you will always be using a 5V PIC. 3. The Output window will show a message Programming/Verify complete if the programming stage was successful. 6

7 4. Debugging of your program can now be started by selecting Launch Debugger from the drop-down button (press little arrow on the right of the button). The first line to be executed is now high-lighted in green. The same buttons used for the simulator can be used to step through your program. Setting Breakpoints: The programmer may need to debug their program to find out what its doing (or not doing, if it is behaving unexpectedly). The MPLAB ICD-3 software allows the user to set ONE breakpoint. Breakpoints allow the user to halt the program at a specific instruction in program memory to allow investigation as to program operation. To provide an example: Assuming your program is still halted; go to the window that shows your source code. Position the mouse over the line that has movlwb' '. Right-click your mouse over the movlw B' ' line and select Toggle Line Breakpoint. An alternative, and quicker, method is to click on the line number on the left of the editor window; a second click will remove the breakpoint. The line should highlighted in RED. This sets a breakpoint to occur when this line is executed. When a breakpoint occurs, THIS instruction will be executed, and then the program will halt. Now RUN your program again by pressing the button. The program will run until the breakpoint is reached. When it does, the program will HALT. The user can now go back and look at the source code and see what instruction was going to be executed next when the program is re-started. The user can then look at Data Registers, Program Memory, or view the Watch Variables that were defined earlier to help in debugging. Task5: Task 6: Step through your program using the debugger. Observe and document what happens to the various Registers including PORTB, TRISB, PORTD, TRISD, PC, W, STATUS, TOGGLE, SEL, Etc. Check out if the changes in the register contents are consistent with the behavior you found when simulating the program. Verify the program runs according to the flowchart by using the debugger to track program execution. Run the program by selecting. Press the RB0/INT button on the PIC development board and observe the sevensegment displays. Document your observation. When done, stop the program by selecting Pause, then close the debugger by selecting. 7

8 IMPORTANT NOTE: During the remaining lab experiments you will be using either the simulator, debugger, or programming modes of MPLAB. There is no need to disconnect the grey cable that connects the ICD-3 programmer from the Laboratory Board. Main Change segment selection Turn on the selected segment Select Bank 1 Set PORTD to all outputs Left shift SEL through carry Return Move SEL to PORTD (7-segment display) Set PORTB pin 0 to input, the rest to outputs Return Set SEL and PORTD to 0x01 Turn on leftmost 7-segment display by setting PORTB pin 1 Set TOGGLE to 1 N Is button on PORTB,0 pressed Is TOGGLE 0? Change segment selection Y Y N Turn on the selected segment This construction is required because of the relatively long period of time you keep the button suppressed Set TOGGLE to 1 Set TOGGLE to 0 8