Led and button with Cortex M3, LM4F120 Microcontroller

This is simple program made on LM4f123 launch pad of texas instruments. One button and a led is interfaced with PORT E pin 0 and Port E pin 1 respectively. Led is initially on, when button is pressed, it will change its state or toggle with a delay of approximately 100ms.

Debugging:

Logic Analyzer: 

Register Window in KEIL

Following is algorithm of the program..

1) Initializes registers of ARM
2) LED is initially on
3) Check if button is on or not
    if button is on, toggle led with 100ms delay
   else nothing

Downloads

Data Sheet

Delay function is a approximation and made by knowing the time a command takes to execute. So it is not precise.  It will take 13333 cycles of while loop for almost 1ms. This fact is used in this program.

Code:

1. // ***** 0. Documentation Section *****
2. // SwitchLEDInterface.c
3. // Runs on LM4F120/TM4C123
4. // Use simple programming structures in C to toggle an LED
5. // while a button is pressed and turn the LED on when the
6. //      Date:    Feb 11, 2016
7. //      Student: Muhammad Awais 2012-EE-506
8. //      Contact Info: Fb/awais12506
9. //      Class:   UTAustinX: UT.6.03x Embedded Systems - Shape the World
11. // ***** 1. Pre-processor Directives Section *****
13. #include "tm4c123gh6pm.h"
15. //Bit specfic adressing for PE0 and PE1
16. //base adress of PORTE is 0x40024000
17. #define SW_PE0   (*((volatile unsigned long *)0x40024004))
18. #define LED_PE1   (*((volatile unsigned long *)0x40024008))
19. // ***** 2. Global Declarations Section *****
21. // FUNCTION PROTOTYPES: Each subroutine defined
22. void PORTE_Init(void);
23. void Delay1ms(unsigned long msec);
24. // ***** 3. Subroutines Section *****
25. //GPIO_PORTE_DATA_R
26. // PE0, PB0, or PA2 connected to positive logic momentary switch using 10k ohm pull down resistor
27. // PE1, PB1, or PA3 connected to positive logic LED through 470 ohm current limiting resistor
28. int main(void){
29. //**********************************************************************
30. // The following version tests input on PE0 and output on PE1
31. //**********************************************************************
33.     PORTE_Init();      // Initlizes PORTE
34. 
    
    
35.     LED_PE1=0x02;      //On LED connected at PE1
36.     Delay1ms(100);     // Delay 100ms
37.   while(1)           //Infinte loop
38.         {    
39.    
40.         if(SW_PE0==0x01)  //If switch is presses
41.         {
42.         LED_PE1^=0x02;    //Toggle LED
43.             Delay1ms(100);
45.         }
46.         else               //else Just on it
47.             LED_PE1=0x02;
48.        
49.   }
51. }
54. /*
55. Descrption: Initilizes PE0==>Input PE1==> Output
56. Input: None
57. Output: None
58. */
59. void PORTE_Init(void)
60. {
61.   volatile unsigned long delay;
62.   SYSCTL_RCGC2_R |= 0x00000010;      // 1) E clock
63.   delay = SYSCTL_RCGC2_R;            // delay to allow clock to stabilize    
64.   GPIO_PORTE_AMSEL_R &= 0x00;        // 2) disable analog function
65.   GPIO_PORTE_PCTL_R &= 0x00000000;   // 3) GPIO clear bit PCTL  
66.   GPIO_PORTE_DIR_R &= ~0x01;         // 4.1) PE0 input,
67.   GPIO_PORTE_DIR_R |= 0x02;          // 4.2) PE1 output  
68.   GPIO_PORTE_AFSEL_R &= 0x00;        // 5) no alternate function      
69.   GPIO_PORTE_DEN_R |= 0x03;          // 6) enable digital pins PE4-PE1
71. }
73. /*
74. Descrption: Uses time of a instruction to delay time
75. Almost 1ms for each cycle
76. Input: Number of ms to delay
77. Output: None
78. */
79. void Delay1ms(unsigned long msec){
80. // write this function
81.     unsigned long i;
82.    
83.   while(msec > 0){
84.     i = 13333;  // this number means 1ms
85.     while(i > 0){
86.       i = i - 1;
87.     }
88.     msec = msec - 1; // decrements every 1 ms
89.   }
91. }

Practical Implementation :