willcharlton
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I am using a PIC24FJ64GA004 on an explorer 16 dev board.
My config bits are:
...set up for XT oscillator with 4xPLL on an 8 MHz crystal oscillator.
In order to verify that the device is indeed running at 32MHz, I set up the following experiment to verify the speed:
When I put my oscilloscope probe on the RB2, the measurement was at 4MHz. I viewed the disassembly break-down and found that the compiler executed the code in the following fashion:
According to the Datasheet, a bset.b, a bclr.b and a bra takes 4 instr cycles - 2 cycles for the bset.b and bclr.b and 2 cycles for the bra.
Since, FOSC = 32MHz, FCY = FOSC/2 = 16MHz and the reading on the pin should be FCY/(#cycles for operation). So the output frequency on PORTBbits.RB2 should be 4 MHz.
It appears as though everything is working, but only if I've done my math and config bits correctly.
Does this seem right to you? Thoughts?
Thanks!
My config bits are:
Code:
_CONFIG1(JTAGEN_OFF & GCP_OFF & GWRP_OFF & BKBUG_ON & COE_OFF & ICS_PGx1 & FWDTEN_OFF & WINDIS_OFF)
_CONFIG2( IESO_OFF & SOSCSEL_SOSC & WUTSEL_FST & FNOSC_PRIPLL & FCKSM_CSDCMD & OSCIOFNC_OFF & IOL1WAY_OFF & I2C1SEL_PRI & POSCMOD_XT)...set up for XT oscillator with 4xPLL on an 8 MHz crystal oscillator.
In order to verify that the device is indeed running at 32MHz, I set up the following experiment to verify the speed:
Code:
while(1)
{
PORTBbits.RB2 = 1;
PORTBbits.RB2 = 0;
}When I put my oscilloscope probe on the RB2, the measurement was at 4MHz. I viewed the disassembly break-down and found that the compiler executed the code in the following fashion:
Code:
444A A842CA bset.b 0x02ca,#2
444C A942CA bclr.b 0x02ca,#2
125: }
444E 37FFFD bra 0x00444aAccording to the Datasheet, a bset.b, a bclr.b and a bra takes 4 instr cycles - 2 cycles for the bset.b and bclr.b and 2 cycles for the bra.
Since, FOSC = 32MHz, FCY = FOSC/2 = 16MHz and the reading on the pin should be FCY/(#cycles for operation). So the output frequency on PORTBbits.RB2 should be 4 MHz.
It appears as though everything is working, but only if I've done my math and config bits correctly.
Does this seem right to you? Thoughts?
Thanks!
