Question

Assembly Language

Using CodeWarrior to create a new project that uses assembly language. Write an assembly program that turns on the red LED at the beginning. It switches to off 2 seconds later and switches back to on after three more seconds. (That is, it stays on for 2 seconds and off for 3 seconds.) This switching process lasts forever. Use a loop (or nested loops) for each of the 2/3-second delay where the loop body of the inner-most loop should contain only multiple instances of the NOP instruction. Use trial-and-error in adjusting the loop iterations to achieve the delay. Write down instructions in the (nested) loops of your program, identify the number of clock cycles needed for each instruction in the loops, and calculate the total number of cycles to get the amount of delay. Use that information to calculate the clock speed of the CPU in MHz, given that the clock speed is an integer in MHz.

Hint: You may use the DBNE instruction for the loop control. In order to find out the number of clock cycles for a particular HCS12 CPU instruction, you may either get it from the data sheet or use the Full Chip Simulation in CodeWarrior, in case you have trouble determining the proper machine code version from the data sheet.

Answer 1

int ledPin1 = 5; // the number of the LED pin
int ledState1 = LOW; // ledState used to set the LED
unsigned long previousMillis1 = 0; // will store last time LED was updated
long OnTime1 = 2000; // milliseconds of on-time
long OffTime1 = 2000; // milliseconds of off-time

int ledPin2 = 6; // the number of the LED pin
int ledState2 = LOW; // ledState used to set the LED
unsigned long previousMillis2 = 0; // will store last time LED was updated
long OnTime2 = 5000; // milliseconds of on-time
long OffTime2 = 1000; // milliseconds of off-time

void setup()
{
  // set the digital pin as output:
  pinMode(ledPin1, OUTPUT);
  pinMode(ledPin2, OUTPUT);
}

void loop()
{
// check to see if it's time to change the state of the LED
unsigned long currentMillis = millis();

  if((ledState1 == HIGH) && (currentMillis - previousMillis1 >= OnTime1))
  {
   ledState1 = LOW; // Turn it off
   previousMillis1 = currentMillis; // Remember the time
   digitalWrite(ledPin1, ledState1); // Update the actual LED
  }
  else if ((ledState1 == LOW) && (currentMillis - previousMillis1 >= OffTime1))
  {
   ledState1 = HIGH; // turn it on
   previousMillis1 = currentMillis; // Remember the time
   digitalWrite(ledPin1, ledState1);   // Update the actual LED
  }
  
  if((ledState2 == HIGH) && (currentMillis - previousMillis2 >= OnTime2))
  {
   ledState2 = LOW; // Turn it off
   previousMillis2 = currentMillis; // Remember the time
   digitalWrite(ledPin2, ledState2); // Update the actual LED
  }
  else if ((ledState2 == LOW) && (currentMillis - previousMillis2 >= OffTime2))
  {
   ledState2 = HIGH; // turn it on
   previousMillis2 = currentMillis; // Remember the time
   digitalWrite(ledPin2, ledState2);   // Update the actual LED
  }
}