Timer Functions - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 382

else{

TC5 15 LoCnt;

HiorLo 5 1;

}

}
The OC5 interrupt vector is set up using the following function (in vectors.c):
extern void near oc5ISR(void);
#pragma CODE_SEG __NEAR_SEG NON_BANKED
#pragma CODE_SEG DEFAULT // Change code section to DEFAULT.
typedef void (*near tIsrFunc)(void);
const tIsrFunc _vect[] @0xFFE4 5 {

oc5ISR

};
Using the OC5 interrupt to restart the subsequent OC5 operations allows the HCS12 to
continue to perform other operations.

▲

Example 8.5
▼

Write a function to generate a time delay that is a multiple of 1 ms. Assume that the
E-clock frequency is 24 MHz. The number of milliseconds is passed in Y. Also write an in-
struction sequence to test this function.
Solution: There are many ways to create a 1-ms time delay using the output-compare function.
One method is
• Set the prescaler to TCNT to 8.
• Perform the number of output-compare operations given in Y with each operation
creating a 1-ms time delay. The number to be added to the TC0 register is 3000
(3000 3 8 4 24,000,000 5 1 ms).
The corresponding assembly function is as follows:
delayby1ms pshd

movb #$90,TSCR1 ; enable TCNT and fast flag clear

movb #$03,TSCR2 ; configure prescaler to 8

bset TIOS,OC0 ; enable OC0

ldd TCNT

again0 addd #3000 ; start an output-compare operation

std TC0 ; with 1-ms time delay

wait_lp0 brclr TFLG1,OC0,wait_lp0

ldd TC0

dbne y,again0

puld
rts
The C language version of the function and its test program are as follows:
#include “c:\cwHSC12\include\hcs12.h”
void delayby1ms(int k);
void main (void)