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crushneck
Joined: 27 Nov 2005
Posts: 29
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| Will Changing of Crystal value effect the circuit? |
 Posted: Tue Jul 04, 2006 8:35 am |
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is there a need to change anything if i change the crystal value from 20Mhz to 30Mhz? to my circuit? will that effect the accuracy of voltage reading?
| Code: | #include <18F452.h>
#device adc=10
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)//< change to 30Mhz crystal
#use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,ERRORS)
#include <lCD420.c>
void main() {
long int result;
long int result2;
float adcresult;
float adcresult2;
lcd_init();
SETUP_ADC_PORTS(AN0_AN1_VSS_VREF);
setup_adc(ADC_CLOCK_DIV_8);
while (TRUE) {
lcd_gotoxy(1,1); //see note about this bit below
printf(lcd_putc, ">>ADC<<");
{
set_adc_channel(0);
delay_us(20);
result = read_adc();
adcresult = 0.0;
adcresult = (float)result * (5.0/1024.0);
adcresult = adcresult*(1.0);
lcd_gotoxy(1,3);
printf(lcd_putc, "ADC (V): %5.3fV", adcresult);
}
{
set_adc_channel(1);
delay_us(20);
result2 = read_adc();
adcresult2 = 0.0;
adcresult2 = (float)result2 * (3.0/1024.0);
adcresult2 = (adcresult2 /1000.0) * (1000.0);
lcd_gotoxy(1,2);
printf(lcd_putc, "ADC (I): %5.2fA", adcresult2);
}
}
} |
Last edited by crushneck on Tue Jul 04, 2006 8:46 am; edited 2 times in total |
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asmallri
Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia
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| Posted: Tue Jul 04, 2006 8:42 am |
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First of all, the original configuration is 20MHz not 20KHz. I assume you meant can you change to 30MHz and the answer is no you cannot. The maximum crystal frequency supported by the PIC18F452 is 20MHz.
You can get up to 40MHz by using the internal PLL x 4 multiplier. To get 30MHz you would use a 7.5MHz crystal and set the fuse for H4 instead of HS. Similarly to operate at 40MHz you would use a 10MHz crystal and the H4 fuse.
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Regards, Andrew
http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!! |
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crushneck
Joined: 27 Nov 2005
Posts: 29
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| Posted: Tue Jul 04, 2006 8:45 am |
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| oops sorry typo error.its not khz...i mean 20Mhz and 30Mhz |
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