Solutions to Homework Assignment #6
Calculations for timing requirements
The Timer Overflow is used to monitor the timing requirements.
One period time for the timer to overflow = 41.2ns * 65536 = 2.73ms
For 8ms delay → 8/2.73 = 3 TOF interrupts
Algorithm /code
#include <mc9s12dp256.h>
#pragma abs_address:0x1000
unsigned long int result = 0;
#pragma end_abs_address
int counter = 0;void main (void) {
ATD1CTL2 = 0x82;//enable interrupt on series complete
ATD1CTL3 = 0x40;//Set conversion sequence length to 8
ATD1CTL4 = 0x05;//Set 10-bit resolution
ATD1CTL5 = 0x83;//Right-justified, unsigned results, conversion
TFLG2 = 0x80;//clear TOF flag by writing 1
TSCR1 = 0x80;//enable timer
TSCR2 = 0x80;//enable timer over flow interrupt
asm("cli"); //Enable interrupts.
while(1) { if (counter == 3) {
while (ATD1STAT1 != 0xFF); //Wait for all CCF flags to go high
// indicating a complete sequence.
//Perform average of 8 converted values and place in result.
result = (ATD1DR0 + ATD1DR1 + ATD1DR2 + ATD1DR3
+ ATD1DR4 + ATD1DR5 + ATD1DR6 + ATD1DR7)/8;
ATD1CTL5 = 0x83;//Clear ATD flags (SCF, CCFs)
counter = 0;//Reset the overflow counter
}
}
}
#pragma interrupt_handler TOF_ISR
void TOF_ISR(void) {
TFLG2 = 0x80;//Clear TOF flag
counter = counter+1;//Increment TOF counter
}
#pragma abs_address:0x3E5E
