Basic Embedded Software C Review Using MPLAB SIM. Loops. Embedded Systems Interfacing. 25 August 2011

Transcription

1 25 August 2011

2 Basic Embedded Software Structure No Operating System to Return to Could Let Program Execute and Reset, But That s Not Efficient Main Function Initialization Code Endless Loop

3 The while Loop Basic Embedded Software Logic Operators Relational Operators The Code while(x) { //Code in the loop } As long as x equals a logical 1 (TRUE), the loop will repeat and the Code in the loop will be executed

4 The Endless while Loop Logic Operators Relational Operators The endless while loop is given by while(1) { //endless loop code here }

5 The Endless for Loop Logic Operators Relational Operators The endless for loop is given by for(;1;) { //endless loop code here } for(; ; ){} also works

6 The Endless do-while Loop Logic Operators Relational Operators The endless do-while loop is given by do { //endless loop code here }while(1);

7 The Endless goto Loop Logic Operators Relational Operators The endless goto loop is given by endless; //endless loop statements goto endless;

8 Logic Operators Basic Embedded Software Logic Operators Relational Operators Often used with relational operators TRUE is a non-zero result FLASE is a zero result is the logical OR operatior && is the logical AND operator! is the logical NOT operator

9 Relational Operators Basic Embedded Software Logic Operators Relational Operators Converts numeric data to Boolean data == is the equal to operator; not to be confused with the assignment operator =! = is the not equal to operator > is the greater than operator >= is the greater than or equal to operator < is the less than operator <= is the less than or equal to operator

10 MPLAB SIM Select MPLAB SIM using Debugger Select Tool MPLAB SIM Select settings under Debugger Settings Animate Set the rate at which you want the animation to run by positioning the slider between 0 and 5.0 sec Use the Debugger Animate button on the tool bar or

11 (cont d) Basic Embedded Software

12 (cont d) Basic Embedded Software The Watch window can be updated with real-time updates The Watch window is updated on program halt To enable updates, check the Enable Realtime watch updates box Move the slider to choose an update increment

13 Intoduction to Timer Basic Embedded Software The animator does not show exactly how the program will run. the PIC24 runs at 32 MHz, so a program that turned an LED on and off would go too quickly for our eyes to see. We can introduce a delay in our program using the SIM

14 SIM 1 Timer 1 is our first peripheral model It is controlled by 3 special-function registers TMR1 - Contents of 16-bit timer value TCON1 - Configuration register for timer; i.e. activation and operating mode PR1 - Peridoic reset value

15 Timer 1 (cont d) Basic Embedded Software

16 Timer 1 (cont d) Basic Embedded Software Timer 1 activated: TON = 1 MCU Clock as source: TCS = 0 Pre-scaler (1:256): TCKPS = 11 No gating or synch: TGATE = 0, TSYNCH = 0

17 Timer 1 (cont d) Basic Embedded Software We set T 1CON = 0b This is T 1CON = 0x8030

18 Setting the Delay Basic Embedded Software The total delay is Solving for DELAY gives T delay = 2 F OSC 256 DELAY. DELAY = T delay F OSC = 512 = 16, 000

19 Example Code Basic Embedded Software #include<p24fj128ga010.h> #define DELAY #define TRUE 1 int main(void) { //Initialize the control registers TRISA=0xff00; //PORTA pin 0..7 as output T1CON=0x8030; //TMR1 on, prescale 1:256, tclk/2

20 Example Code (cont d) //main application loop while(true) { // 1. Turn on pin 0..7 and wait sec PORTA=0xff; TMR1=0; //Restart the count while(tmr1<delay) { //Just wait }

21 Example Code (cont d) // 2. Turn off pin 0..7 and wait sec PORTA=0x00; TMR1=0; //Restart the count while(tmr1<delay) { //Just wait } }//main application loop }//main

22 Starting the Go to Debugger Settings Osc/trace and select Trace All Go to View Simulator Logic Analyzer

23 (cont d) Add signals using Channel button Run, Stop, and view results