[Solved] dsPIC33EP: Input Capture at Low Frequency..

Dear All, I am using dsPIC33EP512MU810 for Input Capture running 60MHz with Timer 3 .Code working fine above 1KHz. Means Frequency 1KHz shown on 1KHz on LCD. I have unable modify code for 10Hz to 250Hz . Is it possible to modify for such a low frequency for Input Capture ?Please Check attachment.. --TS9

Thanks for Update..
 

• The easy way: use the prescaler to scale the clock down to not more than 600 kHz.

How to slow down and calculate clock (For 600KHz) ? 
 

 
void Timer3Init(void)
{
 TMR3 = 0;
 T3CONbits.TON = 0;
 T3CONbits.TCS = 0; // Set Timer freq = Fcy/2
 T3CONbits.TCKPS = 0; // prescale 1:1
 T3CONbits.TGATE = 0; 
 T3CONbits.TSIDL = 0;
 T3CONbits.TON = 1; //Timer 3 Enable
}
 

du00000001
Set timer3's prescaler to 1/256. this will result in a min. capture frequency < 5 Hz while still delivering sufficient numberical resolution @ 250 Hz.

OK..
Means TCKPS= 0x11 will solve the issue?
With Fosc= 60MHz.

What will be Mathematical Expression Counts/Frequency from cap2 - cap1 in code as attachment in Msg # 1 ?

frequency = ((60000000/256)/counts);

I have tested on Setup. "Count" variable overflow below 100Hz.


Any Solution for that..?

Thanks for update..
 
1)
My "Count" variable is unsigned int and 234375 is greater than 65536.
2)
Also check my OSCInit().
3)
// Period = (1/FREQ) / (1/Fosc/2)
// FREQ = (Fosc/2)/Period
// Fosc/2 = 120MHz/2 = 60MHz
 
Something might be wrong here.

 
unsigned int cap1; // first capture variable
unsigned int cap2; // second capture variable
char results[100];
 
void Timer3Init(void)
 
{
 TMR3 = 0;
 T3CONbits.TON = 0;
 T3CONbits.TCS = 0; // Set Timer freq = Fcy/2
 T3CONbits.TCKPS = 0x11; // prescale 1:256
// T3CONbits.TCKPS = 0; // prescale 1:1
 T3CONbits.TGATE = 0; 
 T3CONbits.TSIDL = 0;
 T3CONbits.TON = 1; //Timer 3 Enable
}
 
 
 
void __attribute__ ((__interrupt__, no_auto_psv)) _IC1Interrupt(void)
{
 cap1 = IC1BUF; // Read and save off first capture entry
 cap2 = IC1BUF; // Read and save off second capture entry
LED2 ^= 1;
 IFS0bits.IC1IF = 0 ; // Reset respective interrupt flag
}
 
// To Run Oscillator 120MHz
void OSCInit(void)
{
// Configure PLL prescaler, PLL postscaler, PLL divisor
// ((8Mhz / N1) x 60) / N2 = 120Mhz
// FOSC = 120Mhz
// Fcy = 120Mhz/2 = 60Mhz = 60MIPS
 
 PLLFBD = 58; // M=60
 CLKDIVbits.PLLPOST=0; // N2=2
 CLKDIVbits.PLLPRE=0; // N1=2 
 
// Initiate Clock Switch to Primary Oscillator with PLL (NOSC=0b011)
 __builtin_write_OSCCONH(0x03);
 __builtin_write_OSCCONL(OSCCON | 0x01);
 
// Wait for Clock switch to occur
 while (OSCCONbits.COSC!= 0b011);
 
// Wait for PLL to lock
 while (OSCCONbits.LOCK!= 1);
}
 

Will overflow @ about 3.6 Hz.

How you calculate overflow @3.6Hz ?
Please See entire code...as attachment ..

You can also use 32-bit input capture. They call it "cascade mode" in the docs.

TS9
@NorthGuy..
Is there any Example program for that.?

There's an FRM chapter on Input Capture:
 
http://ww1.microchip.com/...eviceDoc/70000352D.pdf

@du00000001...

I will check then update to you tomorrow.

Repeated