Page 444 - Programming Microcontrollers in C

A Clock Program 429

pulled together into a single listing. Several items have been moved
around in this listing to make the whole program easier to follow.

#include “mmc2001.h”
#include “timer.h”
#include “intctl.h”
#include “serial.h”

#define TIME_COUNT 511
#define MAX_SECONDS 59
#define MAX_MINUTES MAX_SECONDS
#define MAX_HOURS 12
#define MIN_HOURS 1
#define FAST_AUTOVECTOR 0x3000002c
#define TWO_MS 15
#define BAUD_RATE 38400

#define hi(x) ((x)/10+’0')
#define lo(x) ((x)%10+’0')

/* function prototypes */
void output_time(void);
void keep_time(void);
void reset_time(void);
void pit_init(void);
void pit_isr(void);
void handler(void);

/* external—global variables */
WORD seconds,minutes,hours,count;

/* the main applications program. count is incremented in
the isr every two milliseconds. Therefore, this routine
must be executed at least once every two milliseconds to
keep the outputs to the serial port smooth. */
void keep_time(void)
{
if(count>TIME_COUNT)
{
count=0;
if(++seconds>MAX_SECONDS)
{
seconds=0;
if(++minutes>MAX_MINUTES)
{