ECE383- Microcomputers – Lab 4  MPLAB Introduction and PIC24 Assembly Language   Solved

 

Goals: The goals of this lab are to introduce students to basic PIC24 assembly language, usage of the MPLAB Integrated Development Environment (IDE) and associated tools. 

 

1.    Introduction 
 

 

This lab introduces the Microchip MPLAB Integrated Design Environment. All files referenced in the lab are assumed to be in C:\microchip\chap3. The tasks in this lab are:

 

 

•       Use        MPLAB            to         simulate          the       PIC24   assembly         language         program          in         the

C:\microchip\chap3\mptst_word.mcp project to become familiar with the MPLAB environment.

•       Implement some simple programming tasks using PIC24 assembly language.

 

This lab requires you to capture portions of the screen. The lab computers use the Windows operating system. This includes the “Snipping Tool” that may be used to capture portions of the screen. Other third party tools are also available.

 

As always, read through the entire lab and scan the supplied files before starting work. The reporting requirements have you verify computations performed by the assembly language program. In all cases, make it easy for the TA to verify your computations by showing your work. NOTE: When writing MPLAB assembly language programs, do not use variable names a or b as these are reserved names. All hand calculations requested should be shown on a separate piece of paper in the lab report.

 

2.    Pre-lab 
 

For this lab assignment, Task1 and Task 2 should be completed as a pre-lab assignment prior to your assigned lab time. You may also complete all the tasks (including Task 3 and Task 4) prior to the lab time. This may reduce your time in the lab, but is not required.

 

TA check: As soon as you enter lab, provide the TA with a pre-lab report that includes the complete assembly language programs. Lab time will be devoted to debugging the program execution and correcting any errors within MPLAB noted by the lab instructor. Make sure your group member names and date are on the pre-lab report.

 

3.    TASK 1: MPLAB Introduction 
 

Perform the following steps:

 

•       Copy the files in C:\microchip\chap3\ to a suitable directory on your network drive or hard disk. Make sure the directory you use has no spaces in the directory path. An example of a good directory name to

use would be C:\temp\username where “username” is your unique login name.

•       Start the MPLAB IDE. Use Project->Open and open the mptst_word.mcp project located in your directory.

•       Use Configure->Select Device to select the PIC24HJ128GP502 device for your processor.

•       Use Project->Build All (Ctrl+F10) to assemble the program. If the source file is not already open, double- click on the mptst_word.s source file to open it.

•       After the project is assembled, use View->Program Memory and open the program memory window. Scroll the window until you find your program in memory. This should start at location 0x204.

•       Use View->File Registers to view data memory. Scroll to location 0x800, which is where your variables will start.

•       Use View->Special Function Registers to view the special function registers (W0-W15, etc.).

•       Open a watch window (View->Watch) and use Add Symbol and Add SFR to watch variable values and special function register values, respectively, of the i, j, k variables and the W0 (WREG0) special function register.

•       Use Debugger->Select Tool->MPLAB Sim to select the MPLAB Simulator.

•       Use Debugger->Step Over (F8) to single step the program. Watch both the memory locations and watch window locations, and correlate their changing values with the instructions being executed.

 

TA check: Show the TA the task 1 results including the final state of the program, data memory, and the watch window. Use a screen capture tool to capture these windows and include them in your lab report. Include your source assembly language program in your lab report.

 

Modify the avalue equate (statement .equ avalue, 2047) to be the last four digits of your student ID. Reassemble the program and re-simulate it. Take a screen shot of both the Watch window contents and the memory window contents. In your report, you must show calculations that verify the screen shot values match the expected result (note, avalue is in decimal, as are the last four digits of your student ID: the values displayed in the file registers window are in HEX).

 

TA check: Show the TA the modified task 1 results including the final state of the program, data memory, and the watch window. Use a screen capture tool to capture these windows and include them in your lab report. Include your source assembly language program in your lab report.

 

4.    TASK 2: myadd.s 
 

Use Project->Save Project As and save the mptst_word project as a new project named myadd. Save the mptst_word.s file as myadd.s. Right-click on the mptst_word.s file in the left-hand workspace window and use the Remove option to remove it from the myadd project. Right click on the Source Files and use Add Files to add the   myadd.s   file   to   the   project.   Edit   the   myadd.s   file   and   remove all   of   the   instructions   from mov #avalue, W0 through mov WREG,k. You can now use this file as a start for a new program.

 

Your CWID student number is an eight digit number Y7Y6Y5Y4Y3Y2Y1Y0. For this task we will consider this to be an eight digit hexadecimal number.

 

Write a program to add the four digit hex number formed by 0xY3Y2Y1Y0 to the four-digit hex number formed by

0xY7Y6Y5Y4. Reserve space for two 16-bit variables in data memory named lsp and msp to hold the hex values 0xY3Y2Y1Y0 and 0xY7Y6Y5Y4 respectively. Reserve space for a variable named sum to hold the sum of lsp and msp.

 

The following C code describes the program. You must translate each line of the C program to corresponding assembly instruction(s).

 

uint8 aa=100, bb=22; uint16 lsp, msp, sum; 

 

lsp = 0xY3Y2Y1Y0;       // Four digits of CWID treated as hex msp = 0xY7Y6Y5Y4;       // Four digits of CWID treated as hex sum = lsp + msp; 

 

sum = sum + aa + bb; 

 

Use the watch window to watch variables aa, bb, lsp, msp, and sum. Also, use the data memory window to monitor the memory locations corresponding to these variables.

 

TA check: Show the TA the task 2 results including the final state of the program, data memory, and the watch window. Use a screen capture tool to capture these windows and include them in your lab report. Include your source assembly language program in your lab report. Since you will be working in teams in the lab, use only one student number for each team. 

 

5.    TASK 3: mysub.s 
 

 

Create a project named mysub using the same procedure given in Task 2 (Project ->Save Project As, etc.) corresponding assembly language file named mysub.s. Using digits Y5Y4Y3Y2Y1Y0 from your student ID, write an assembly language program that implements the following C program. You must translate each line of the C program to assembly instruction(s).

 uint16 xx=0xDEAD, yy=0xBEEF; 

              uint8 i, j, k, l, m; 

 

i = Y1Y0; j = Y3Y2; k = Y5Y4; l = i + k; m = j – l; xx=xx-yy-m; 

 

Variables i, j, k, l, m are all 8-bit (byte) variables and xx and yy are 16-bit variables.  Y1Y0, Y3Y2 and Y5Y4 are considered as decimal numbers for this task.  Use the watch window to watch variables i, j, k, l, m, xx, and yy. Also, use the data memory window to monitor the memory locations corresponding to these variables. Write your program, simulate it, and verify that you calculate the correct results.

 

Hint: If you experience the error “Link Error: Cannot access symbol (xx) at an odd address”, initialize 16-bit variables first and then 8-bit variables. That is, all variables defined using the .space 2 directive should appear before variables defined using the .space 1 directive.

 

Give the value of the flags after the execution of each instruction. Assume that W0 = j and W1 = l.

 

Instruction 

 
 
 
Value of flags 
 
C 
Z 
 
OV 
N 
ADD.B W0,W1,W0
 
 
 
 
 
SUB.B W0,W1,W0
 
 
 
 
 
 

TA check: Show the TA the task 3 results including the final state of the program, data memory, and the watch window. Use a screen capture tool to capture these windows and include them in your lab report. Include your source assembly language program in your lab report.

 

6.    TASK 4: mylogicops.s 
 

Create a project named mylogicops using the same procedure given in Task 2 (Project ->Save Project As, etc.) corresponding assembly language file named mylogicops.s. Write an assembly language program that implements the following C program. You must translate each line of the C program to assembly instruction(s).

 

uint8 u8_a, u8_b, u8_c, u8_d, u8_e, u8_f; uint16 u16_x=0x0001; 

 

u8_a=0xAF; u8_b=0x50; 

 

u8_c= u8_a & u8_b; u8_d= u8_a | u8_b; u8_e= u8_a ^ u8_b; u8_f=~u8_a; 

u16_x=~u8_d | (u16_x & u8_c); 

 

Use the watch window to watch variables u16_x, u8_a, u8_b, u8_c, u8_d, u8_e, and u8_f. Also, use the data memory window to monitor the memory locations corresponding to these variables. Write your program, simulate it, and verify that you calculate the correct results.

 

In addition to simulating your program within MPLAB, you must download your program to your PIC24 hardware (the Microstick II) and demonstrate the execution of your program on hardware to the TA. Make sure the Microstick II development board is attached to a USB port on your computer and make sure the slider switch on the board is set to position A. With the mylogicops project open, use the following steps 

 

•       If not already selected, use Configure->Select Device to select the PIC24HJ128GP502 device for your processor.

•       Use Debugger->Select Tool->Starter Kit on Board to select the Microstick II as the target. You should see messages in the MPLAB Output window indicating a successful connection to the Microstick II board.

•       Use Project->Build All (Ctrl+F10) to assemble the program. If the source file is not already open, double- click on the mylogicops.s source file to open it.

•       Use Debugger->Program to download your code to the Microstick II. You should see messages in the MPLAB Output window indicating successful programming of the Microstick II board.

•       After the project is downloaded, use View->Program Memory and open the program memory window.

•       Scroll the window until you find your program in memory. This should start at location 0x204.

•       Use View->File Registers to view data memory. Scroll to location 0x800, which is where your variables will start.

•       Use View->Special Function Registers to view the special function registers (W0-W15, etc.).

•       Open a watch window (View->Watch) and use Add Symbol and Add SFR to watch variable values and special function register values, respectively, of the all of the defined variables and the W0 (WREG0) special function register.

•       Set a breakpoint on the first line of your assembly language program by double clicking on the line in the assembly language program.

•       Begin the execution of your program by selecting Debugger->Run.

•       Use Debugger->Step Over (F8) to single step the program. Watch both the memory locations and watch window locations, and correlate their changing values with the instructions being executed.

 

TA check: Show the TA the task 4 results including the final state of the program, data memory, and the watch window for both the MPLAB PIC24 simulator and the PIC24 hardware. Use a screen capture tool to capture these windows and include them in your lab report. Include your source assembly language program in your lab report. 

 

7.    Report 
 

At the next lab period, provide the TA a printed copy of the lab report following the ECE383 Lab report Template given on the class website. Each lab group will submit one joint lab report to the TA. Your report should have the reporting requirements needed for Tasks 1, 2, 3, and 4. The TA will take off a significant number of points (up to 15% from total lab grade) if your assembly language source does not have the required comments. The comments should indicate which assembly language source lines implement which C statements.