Real time clocks, out of the question?

[Nathan]

Yes, EasyC does have timers, six of them. I believe we have used up to three at once, and they all work fine.

What exactly isn't working for your? Could you post your code?

Thanks,
Nathan

[evan_wilson]

Well, the problem is that I don't have any. Without EasyC, I just have the arm calculating based on loop counting. Multiples of 26.2 ms. There's no way I can switch to EasyC this year. I guess that would be a logical solution for next year.

Is there anyone here who has ever written a timer and interrupt routine for a real time clock? That's really the only thing I could worry about anyways. Otherwise I'll just have to stick with loop counting.

[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.
  }

[evan_wilson]

Thank you very much. I hope my assembly serves me well.
I think I can dig up the differences in the new controller.

Want to be a mentor...

just kidding.

[Astronouth7303]

Setting up just a realtime clock isn't that hard. I was thinking of doing it myself. I just have to figure out how to configure which timer to achieve something reasonable.

[Mike Bortfeldt]

Here is the code we used for a "clock". It uses Timer 2 and has a number of options for flexibility. It is not a "real time clock" in the sense that it doesn't compute hour/minute/second but works off clock "ticks", which for a 2 minute match, or a 15 second autonomous, works fine for us. By default, it's configured to count milliseconds (1 tick = 1 millisecond), but has 2 other predefined options for increased accuracy.

Mike

[Mark McLeod]

In teaching timers I use a demonstration program to calculate all the possible timer prescaler/postscaler combinations for a given Hertz or time period. It's an easy beginner exercise to write such a program for the PIC (or VB), and also can be used to teach them about maintaining the Master processor communication leading to an easy elimination of the Master handshake.

Here's a sample output calculating 2400 Hz used with an LCD display off a digital output.