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object01
Joined: 13 May 2004
Posts: 90
Location: Nashville, TN
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| Slow clock on PIC18F2620 |
 Posted: Thu Feb 17, 2005 12:45 pm |
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After upgrading to the latest CCS compiler and ICD-U40 firmware, we seem to be having a problem with 2620's. We've loaded a Wizard-generated program (plus some LED blinker code) into the PIC and are observing a clock rate of about 246KHz on CLKOUT, regardless of the value we use for #use delay.
Can anyone help us figure out whether this is a CCS problem or not?
--
Jeff S.
| Code: | //////////// main.c
#include "main.h"
void main() {
setup_adc_ports(NO_ANALOGS|VSS_VDD);
setup_adc(ADC_OFF|ADC_TAD_MUL_0);
setup_spi(FALSE);
setup_wdt(WDT_OFF);
setup_timer_0(RTCC_INTERNAL);
setup_timer_1(T1_DISABLED);
setup_timer_2(T2_DISABLED,0,1);
setup_timer_3(T3_DISABLED|T3_DIV_BY_1);
setup_comparator(NC_NC_NC_NC);
setup_vref(FALSE);
while (TRUE) {
output_toggle(PIN_A0);
}
}
///////////////// main.h
#include <18F2620.h>
#device adc=8
#use delay(clock=8000000)
#fuses NOWDT,WDT128,INTRC, NOPROTECT, NOIESO, NOBROWNOUT, BORV21, NOPUT, NOCPD, STVREN, DEBUG, LVP, NOWRT, NOWRTD, NOEBTR, NOCPB, NOEBTRB, NOWRTC, NOWRTB, FCMEN, NOXINST, NOPBADEN, LPT1OSC, MCLR |
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object01
Joined: 13 May 2004
Posts: 90
Location: Nashville, TN
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| Posted: Thu Feb 17, 2005 1:07 pm |
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I examined the lst's produced by this code, and aside from the instructions generated for setup_comparator(), there is absolutely no difference in the .lst's when I change the #use delay() directive. I'm not savvy enough to know whether this is normal.
--
Jeff S. |
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libor
Joined: 14 Dec 2004
Posts: 288
Location: Hungary
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| Posted: Thu Feb 17, 2005 1:51 pm |
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#use delay does not generate code, it is simply a directive that informs the compiler how fast it should expect to processor running so it genenerates the proper delay cycles when you use delay_us(), delay_ms(), and serial comm. instructions.
It is not quite clear for me what 'change' did you expect of changing the #use delay value. It does not sets the clock speed. |
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object01
Joined: 13 May 2004
Posts: 90
Location: Nashville, TN
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| Posted: Thu Feb 17, 2005 1:54 pm |
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| libor wrote: | #use delay does not generate code, it is simply a directive that informs the compiler how fast it should expect to processor running so it genenerates the proper delay cycles when you use delay_us(), delay_ms(), and serial comm. instructions.
It is not quite clear for me what 'change' did you expect of changing the #use delay value. It does not sets the clock speed. |
According to readme.txt,
"A new function SETUP_OSCILLATOR controls and returns the state of the
internal RC oscillator on some parts. See the devices .h file for
valid options for a particular device. Note that is INTRC or INTRC_IO
is specified in #fuses and a #USE DELAY is used for a valid speed option,
then the compiler will do this setup automatically at the start of main()."
So I would expect to see some kind of assembly change, because I satisfy the two conditions mentioned there. We have always used #use delay() to govern the internal oscillator speed of our PICs in the past.
--
Jeff S. |
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object01
Joined: 13 May 2004
Posts: 90
Location: Nashville, TN
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| Posted: Thu Feb 17, 2005 4:10 pm |
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CCS Support suggested that I switch the #use delay() and #fuses lines, so that #use delay() would be aware that I was using INTRC. Did that, and the problem was solved. I also told them the Project Wizard was responsible for generating the odd code.
--
Jeff S. |
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jcjneudo
Joined: 21 Feb 2005
Posts: 4
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| 32MHz operation with 18F4620 |
| Posted: Tue Feb 22, 2005 9:25 am |
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Having the "#use delay" after the "#fuses" seems to work, at least for 8MHz. Unfortunately, it does not seem to do the right thing for 32MHz operation--there does not seem to be any way to enable the PLL with the internal oscillator (at least using library functions).
Any work-arounds?
(I'm using PCWH v 3.212) |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Feb 22, 2005 12:22 pm |
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| Quote: | there does not seem to be any way to enable the PLL with the
internal oscillator |
Study the 18F8620 data sheet, in the Oscillator section.
"The PLL can only be enabled when the oscillator configuration
bits are programmed for HS mode. If they are programmed
for any other mode, the PLL is not enabled and the system clock
will come directly from OSC1."
Link to the data sheet:
http://ww1.microchip.com/downloads/en/DeviceDoc/39609b.pdf |
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jcjneudo
Joined: 21 Feb 2005
Posts: 4
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| 32MHz with INTOSC on 18F4620 |
| Posted: Wed Feb 23, 2005 7:32 am |
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Umm, the data sheet "PCM PROGRAMMER" posted is for the PIC18F6520/8520/6620/8620/6720/8720. Perhaps the limitation is valid for those chips. But for the PIC18F4620 (see DS39626B), the PLL can be connected to the internal oscillator in software. If the primary oscillator is the internal oscillator (INTOSC), the PLL can be enabled through use of PLLEN in OSCTUNE<6> (see section 2.6.4).
I was finally able to get this working by using the following code, but it would be better if CCS handled it as per the documentation (ie, if you set fuses and delay, the oscillator will be set up automatically before main is called):
| Code: |
#fuses INTRC_IO,NOIESO,NOFCMEN,WDT1,NOWDT,BROWNOUT,NOPUT,NOPROTECT,CCP2C1,NOLVP,NOXINST,NOMCLR
#use delay (clock=32000000)
.
.
.
SETUP_OSCILLATOR(OSC_8MHz,0);
OSCTUNE = 0b01000000;
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Feb 23, 2005 8:35 am |
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OK, but it's understandable that I missed your PIC type, because
this thread was about 18F2620 problems, and you tacked your
problem onto it. I missed seeing the small title on your post. |
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