Frequency measurement using input capture module in dspic30f5011

[KlausST]

Hi,

What about my recommendations of post#19?

Klaus

 

[saikiran@ees]

Hi,
With 32 bit timer and 1:1 prescaler I can't handle the 16 bit lsb and 16 bit msb values.So that I come back to 16 bit timer with 256 prescaler. But with this timer I am getting the values with error like 0.3 to 0.6.So how to reduce the error.

Thanks and Regards
M SAI KIRAN.

 

[KlausST]

Hi,

I don´t understand.

With 32 bit timer and 1:1 prescaler I can't handle the 16 bit lsb and 16 bit msb values.

What´s wrong with it?

I bit more detailes, please.

Klaus

 

[saikiran@ees]

Hi,
With 32 bit timer,the input capture channel captures the 16 bit lsb that is from timer 2.If timer 2 values are maximum then values will be updated into timer 3.But I have only one channel available on my controller as per the design. when I want the higher values the input capture captures the overflow result.So,that why I am uisng 16 bit timer and 256 prescaler.

Thanks and Regards,
M SAI KIRAN.

 

[KlausST]

Hi,

It seems you insist on the 16 bit values.
According the previously made calculations it is not possible to work with 16 bits.
So
* either use the 32 bits for your full desired frequency range
* or use the 16 bit with decreased frequency range. A prescaler won´t change resolution:

There is no way round.

*****

But if you setup the timer to 32 bit mode, you should calaculate with 32 bits. Not 16 bits anymore.

Combine the 16 bits of timer 2 with the 16 bits of timer3 to get a 32 bit value.
Now you have a huge dynamic.

***
You didn´t say where exactley you see a problem .. so I don´t know how to help you.
--> show your code. Describe what test you perform. Describe what result you expect and describe the unecpected result.

****

But I have only one channel available on my controller as per the design

WHAT channel?

Klaus

 

[saikiran@ees]

Hi,

I have configured 2 input capture channels to capture two 16 bits individually( MSB LSB) of 32 bits and timer as 32-bit by combining timer2 and timer3. here is my code
*************** input capture *************************

void IC_INIT(void)
{
	// Register 13-1: ICxCON: Input Capture x Control Register in datasheet  
	IC2CONbits.ICM= 0b011;				// Input Capture Mode Select (Every rising edge)
	IC2CONbits.ICBNE=0;					// Input Capture Buffer Empty Status (Read Only)
	IC2CONbits.ICOV=0;					// Input Capture Overflow Status Flag (Read Only)
	IC2CONbits.ICI= 00;					// Select Number of Captures per Interrupt bits (00 = Interrupt on every capture event)
	IC2CONbits.ICTMR=1;					// Input Capture Timer Select bits 1=TMR2 contents are captured on captured event)
	IC2CONbits.ICSIDL=0;    				// Input Capture Module Stop in Idle Control(0=Input capture module will continue to operate in CPU Idle mode)
	
	IC3CONbits.ICM= 0b011;				// Input Capture Mode Select (Every rising edge)
	IC3CONbits.ICBNE=0;					// Input Capture Buffer Empty Status (Read Only)
	IC3CONbits.ICOV=0;					// Input Capture Overflow Status Flag (Read Only)
	IC3CONbits.ICI= 00;					// Select Number of Captures per Interrupt bits (00 = Interrupt on every capture event)
	IC3CONbits.ICTMR=0;					// Input Capture Timer Select bits 0=TMR3 contents are captured on captured event)
	IC3CONbits.ICSIDL=0;    				// Input Capture Module Stop in Idle Control(0=Input capture module will continue to operate in CPU Idle mode)
	IPC1bits.IC2IP = 5;
	// Register 6-6: IFS1: Interrupt Flag Status Register 1
	IFS0bits.IC2IF = 0;       			// Input Capture Channel 2 Interrupt Flag Status )0=Interrupt bit is cleared
	// Register 6-9: IEC1: Interrupt Enable Control Register 1
	IEC0bits.IC2IE = 1;     			// Input Capture Channel 2 Interrupt Enable bit (1 = Interrupt request enabled) 
	printf("Ic ready\n");
	
}

void __attribute__((__interrupt__,no_auto_psv)) _IC2Interrupt(void)
{
	
		
	LSB = IC2BUF;
	MSB = IC3BUF; 			
	IFS0bits.IC2IF= 0; //Clear bit IC1IF (IFS<2>)

}

****************** timer *****************************

void timer_init(void)
{
 	T2CON			=0;							//disable Timer2
 	TMR2			=0x0000;					        //Timer2 reg
 	PR2				=0xFFFF;						//PR reg of Timer2
 	T2CONbits.TSIDL	= 0;							// configuring timer3
	T2CONbits.TCKPS	= 0b00;	                 			// 1:1 prescaler	
	T2CONbits.T32		= 1;							//Timer2 & Timer3 Configured as 32-bit Timer	
	T3CON			= 0;							//desabling timer3
	TMR3			= 0X0000;					        // TIMER3 REGISTER
	PR3				= 0xFFFF;					// time period						
	IFS0bits.T3IF		= 0;							// clear interrupt flag 
	IPC1bits.T3IP		= 7;							// set interrupt priority
	IEC0bits.T3IE		= 1;							// interrupt enable
	T2CONbits.TON		= ON;						// enable timer2
	T3CONbits.TON		= ON;						// enable timer3
	printf("Timer ready\n");
	
}



void __attribute__((__interrupt__,no_auto_psv)) _T3Interrupt(void)
{	
	IFS0bits.T3IF	= 0;
}

The problem is i'm getting 0 every time in MSB.

Regards
Sai

 

[saikiran@ees]

Hi,
Is there an wrong in my code or Is there any need to short the two channels that I used to get the required output.Otherwise any changes in my program.

Thanks and Regards,
M SAI KIRAN.