pllcon.c

8051试验程序 基础教材

//********************************************************************
//
// Author        : ADI - Apps            www.analog.com/MicroConverter
//
// Date          : November 2001
//
// File          : pllcon.c
//
// Hardware      : ADuC836
//
// Description   : Demonstrates that the CPU can run at different
//               speeds determined by the CD bits in the PLLCON SFR.
//               2 to the power of CD (a 3 bit number), is the divider
//               ratio that determines the clock frequency at which
//               the CPU will run. (CD=0 =>fcore=12.58MHz,
//               CD=7 => fcore=98.3kHz)
//
//	             The program turns on and off the LED approx every
//               70,000 machine cycles. With the higher frequency
//		         (CD=0 =>fcore=12.58MHz) the LED toggles at about
//               16Hz. By pressing the INT0 button the CD bit is
//               incremented (CD=1 =>fcore=6.3MHz) and the LED will
//               toggle at half the frequency as before. At the
//               minimum frequency (CD=7, fcore=700kHz) the LED
//               toggles at 0.125Hz. By pressing INT0 button again
//               CD rolls over to 0 again and the LED
//		         toggles at 16Hz again.
//
//********************************************************************

#include <stdio.h>
#include <ioADuC836.h>

#define adcled P3_bit.P33
#define LED P3_bit.P34		//P3.4 drives red LED on eval board
int i;

#pragma vector=extern0
__interrupt void interrupt_0 ()
{
	LED ^= 1;
	i = 9999;
	PLLCON++;
	PLLCON &= 0x07;
}
void main (void)
{
	PLLCON = 0x00;
	TCON_bit.IT0 = 1;
	IE_bit.EX0 = 1;
	IE_bit.EA = 1;

	while(1)
	{
		LED ^=1;
		for (i = 0; i < 10000; i++)
		{
		}
	}
}