ECE383: Microcomputers – Lab 5 C and PIC24 Assembly Language Programming

Introduction
This lab introduces basic C language programs and equivalent PIC24 assembly language programs. The tasks in
this lab are:
• Implement programming tasks using the C language.
• Implement equivalent programs using the 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 any supplied files before starting work. The reporting
requirements have you verify computations performed by the assembly language or C 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.
This lab will make use of several C header files discussed in the text. These files should be located in the
C:\microchip\lib\include directory on the lab computers. These files were installed as a part of the PIC24 library
available on the class website.

1. Prelab
   For this lab assignment, the programs for Task 1 and 2 should be completed as a pre-lab assignment prior to
   your assigned lab time.
   TA check: As soon as you enter lab, provide the TA with a pre-lab report that includes the complete C and
   assembly language programs. Lab time will be devoted to debugging the program execution and
   correcting any errors noted by the lab instructor. Make sure your group member names and date are on
   the pre-lab report.
2. TASK 1: Basic C arithmetic operations
   For this task you will create multiple C and assembly language projects implementing arithmetic operations.
   Perform the following steps:
   • Start the MPLAB IDE. Use Project->Project Wizard for the creation of an MPLAB project.
   o Step One: Select the device PIC24HJ128GP502.

Step Two: Select the Active Toolsuite as Microchip C30 Toolsuite.
o Step Three: Create a New Project File in a unique directory on the local hard disk
(C:\temp\task1.mcp as an example).
o Step Four: Skip the addition of existing files to the project.
• After the project is open, use Project->Build Options to add the C:\microchip\lib\include directory to the
Include Search Path directory as shown in Figure 1 below.

• Enter the C program below and save it with the name task1.c as a part of the project.

include “pic24_all.h”

uint16 u16_a, u16_b, u16_c, u16_d;
uint8 u8_x, u8_y, u8_z;
void main(void) {
u8_x=0xFF;
u8_y=0x01;
u16_a = 0xFFFF;
u16_b = 0x0001;

u8_z=u8_x+u8_y;
u16_d=(uint16) u8_x + (uint16) u8_y;
u16_c=u16_a+u16_b;
}

Use Project->Build All to compile the program. If the source file is not already open, double-click on
the task1.c source file to open it.
• After the project is compiled, use View->Program Memory and open the program memory window.
Scroll the window until you find your program in memory. Your program should begin at location 0x200.
• 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 (these will appear as WREG0-
WREG15, etc).
• Open a watch window (View->Watch) and use Add Symbol to watch variable values of the all the program
variables. Use Add SFR to watch the SR (status register) special function register value.
• Use Debugger->Select Tool->MPLAB Sim to select the MPLAB Simulator.
• Use Debugger->Step Into (F7) to single step through the program. Watch both the memory locations and
watch window locations, and correlate their changing values with the instructions being executed. For
all three of the arithmetic operations, record the value of the result and the value of the sign/negative
(N), carry (C), zero (Z), and overflow (V) flags. The value of the flags can be determined from the SR
register and are also indicated at the bottom of the MPLAB IDE.
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 language program in your lab report.

3. TASK 2: C Program check_val
   Create an MPLAB project (task2.mcp) containing a C program (task2.c) that counts the number of one bits in a
   16-bit unsigned integer named check_val. The count value should be stored in an 8-bit unsigned variable
   named ones_count. The program should also determine which is the first bit set in the check_val
   variable. The location of the first bit set should be stored in an 8-bit unsigned variable named first_one. For
   example, if check_val=0xF508 then the computed values should be ones_count=7 and first_one=3.
   Hint: Use a for loop and shift right every iteration of the loop to simplify testing of a bit value. You must download
   your program to your PIC24 hardware (i.e. the Microstick II) and demonstrate the execution of your program on
   hardware to the TA.
   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 language program in your lab report.
4. TASK 3: Assembly Language Program check_val
   Create an MPLAB project (task3.mcp) containing an assembly language program (task3.s) that implements the
   equivalent of task 2.
   You must download your program to your PIC24 hardware and demonstrate the execution of your program on
   hardware to the TA.

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 language program in your lab report.

5. TASK 4: Assembly to C Example
   Create a new assembly project and input the assembly code as shown below. See the program results after
   executing the program. Create an MPLAB project (task4.mcp) containing a C program (task4.c) that implements
   the equivalent of the assembly program.
   .include “p24Hxxxx.inc”
   .global __reset
   .bss ; Uninitialized data section
   ; Variables start at location 0x0800
   x: .space 2 ; Allocating space (two bytes) to variable.
   y: .space 2 ; Allocating space (two bytes) to variable.
   count: .space 1 ; Allocating space (one byte) to variable.
   ;……………………………………………………………..
   ; Code Section in Program Memory
   ;……………………………………………………………..
   .text ; Start of Code section
   __reset: ; first instruction located at __reset label
   mov #__SP_init, w15 ; Initialize the Stack Pointer
   mov #__SPLIM_init,W0
   mov W0, SPLIM ; Initialize the stack limit register
   ; __SP_init set to be after allocated data
   ; User Code starts here.
   mov #0x3, w0
   mov.b wreg, count
   mov #0x1, w1
   mov w1, x
   mov #0x3, w2
   mov w2, y
   top:
   cp0.b count
   bra z, done
   cp w1, w2
   bra nz, next
   inc w2, w2
   mov w2, y
   next:
   cp w1, w2
   bra GEU, next2
   add #0x2, w1
   mov w1, x
   next2:
   dec.b count

bra top
done: goto done ; Place holder for last line of executed code
.end ; End of program code in this file
You must download your program to your PIC24 hardware and demonstrate the execution of your program on
hardware to the TA.
TA check: Show the TA the task 4 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 language program in your lab report.

6. Laboratory Report
   No later than a week from the day the lab is performed, 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 (15 points from total lab grade) if your C and assembly language source does
   not have the required comments. The C programs should be appropriately commented. For the assembly
   programs, the comments should indicate which assembly language source lines implement which C statements.
7. GRADING POLICY
8. Completion of the prelab assignment (20%)
9. Completion of Task 1 with results included in lab report (15%)
10. Completion of Task 2 with results included in lab report (15%)
11. Completion of Task 3 with results included in lab report (15%)
12. Completion of Task 4 with results included in lab report (15%)
13. Completeness, quality, and correctness of the lab report (20%)

Source: ECE383: Microcomputers – Lab 5 C and PIC24 Assembly Language Programming