Real time clocks, out of the question?

[Mark McLeod]

Timers are simple to use, no soldering required.
IFI has a white paper on coding timers that goes into the bits and bytes of it all:
http://www.ifirobotics.com/docs/time...004-jan-14.pdf

For a description of the timer library calls see the MPLAB-C18-Libraries.pdf manual under C:\mcc18\doc.

Here's a sample using the timer libraries:

// In user_routines.c
#include <timers.h>
#define CLOCKOFFSET 60535  //Set timer for 4ms
  // Maximum for 16-bit timer 65535 - 5000 (4ms) = 60535
 
/* Use Timer3 (16-bits) to control our clock */
/* timer set to 4 ms */
 
// Call from User_Initialization()
  OpenTimer3(TIMER_INT_ON &
             T3_16BIT_RW &
             T3_SOURCE_INT &
             T3_PS_1_8
             );
 
  WriteTimer3(CLOCKOFFSET);  /* Preload timer to overflow after 4ms */

  // In user_routines_fast.c
  #include <timers.h>
  // globals declared as extern wherever else they are used
  volatile unsigned long Clockms=0; // 1 millisecond clock
  volatile unsigned int Clockds=0; // 1/10 second
  volatile unsigned int Clocksec=0; // 1 second clock
  //etc.
 
 
// In InterruptHandlerLow()
  if (PIR2bits.TMR3IF) /* TIMER 3 INTERRUPT */
  {
    /** This provides us with a clock for timing events **/
    PIR2bits.TMR3IF = 0; /* Clear Timer interrupt flag */
    WriteTimer3(CLOCKOFFSET);  /* Reset Timer to overflow in 4ms */
    Clockms += 4; /* milliseconds */
    Clockds = Clockms / 100;
    Clocksec = Clockms / 1000;
    // etc.
  }