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elellilrah
Joined: 29 Aug 2007
Posts: 14
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| setup_oscillator() on PIC16F688 not working |
 Posted: Fri Jan 30, 2009 2:47 pm |
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I'm trying to get the PIC16F688 to run at 8MHz without success. Using compiler rev 4.085 I've tried the following:
| Code: | #include <16F688.h>
#device adc=8
#FUSES NOWDT //No Watch Dog Timer
#FUSES INTRC //Internal RC Osc
#FUSES NOPROTECT //Code not protected from reading
#FUSES NOBROWNOUT //No brownout reset
#FUSES MCLR //Master Clear pin enabled
#FUSES NOCPD //No EE protection
#FUSES NOPUT //No Power Up Timer
#FUSES IESO //Internal External Switch Over mode enabled
#FUSES FCMEN //Fail-safe clock monitor enabled
#use delay(clock=8000000)
void main()
{
setup_oscillator(OSC_8MHZ);
setup_adc_ports(NO_ANALOGS|VSS_VDD);
setup_adc(ADC_OFF);
setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
setup_timer_1(T1_DISABLED);
setup_comparator(NC_NC_NC_NC);
setup_vref(FALSE);
while(1)
{
}
} |
The list code is:
| Code: | .................... void main()
.................... {
0004: CLRF 04
0005: BCF 03.7
0006: MOVLW 1F
0007: ANDWF 03,F
0008: MOVLW 71
0009: BSF 03.5
000A: MOVWF 0F
000B: MOVF 0F,W
000C: BCF 03.5
000D: BCF 1F.6
000E: MOVLW 00
000F: BSF 03.5
0010: MOVWF 11
0011: BCF 03.5
0012: CLRF 1A
0013: MOVLW 07
0014: MOVWF 19
.................... setup_oscillator(OSC_8MHZ);
0015: MOVLW 71
0016: BSF 03.5
0017: MOVWF 0F
0018: MOVF 0F,W
.................... setup_adc_ports(NO_ANALOGS|VSS_VDD);
0019: BCF 03.5
... |
When I look at the OSC2 pin (pin 2, 16-pin QFN PIC16F688), I only get 2MHz clocking out.
I've tried the following constants with the following results:
OSC_8MHZ - 2 MHz on OSC2
OSC_4MHZ - 1 MHz on OSC2
OSC_2MHZ - 500 kHz on OSC2
OSC_1MHZ - 250 kHz on OSC 2
I've been trying to do some timing measurements and getting numbers 4x lower than I should, causing me to look into this. The numbers above completely explain why I have wrong timing measurements, but now I need to get the PIC running at the right speed. Any suggestions? Thanks!
I'm using the ICD-U40 to program the PIC16F688 chip, running @ 4V. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jan 30, 2009 3:00 pm |
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| Quote: |
When I look at the OSC2 pin (pin 2, 16-pin QFN PIC16F688), I only get
2MHz clocking out. |
See this section of the 16F688 data sheet:
| Quote: |
3.5.1 INTOSC AND INTOSCIO MODES
In INTOSC mode, OSC1/CLKIN is available for general
purpose I/O. OSC2/CLKOUT outputs the selected
internal oscillator frequency divided by 4. |
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elellilrah
Joined: 29 Aug 2007
Posts: 14
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| All clear, now |
| Posted: Fri Jan 30, 2009 5:04 pm |
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| PCM programmer wrote: | | Quote: |
When I look at the OSC2 pin (pin 2, 16-pin QFN PIC16F688), I only get
2MHz clocking out. |
See this section of the 16F688 data sheet:
| Quote: |
3.5.1 INTOSC AND INTOSCIO MODES
In INTOSC mode, OSC1/CLKIN is available for general
purpose I/O. OSC2/CLKOUT outputs the selected
internal oscillator frequency divided by 4. |
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Thanks, PCM...it's right there, in front of me, if I knew where to look. Ah, data sheet details.
And, that suggestion lead me to timer1 having it's primary clock divided by 4 as well, hence why I got such low numbers.
Now I've got to figure out how to count higher than 255 with counter0. Thanks! |
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