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antosci
Joined: 29 Apr 2013
Posts: 13
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| operative clock problem |
 Posted: Mon Nov 03, 2014 5:42 pm |
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hi, i'm trying to blink a led... a simply led blinking, cause i attempted to communicate trough rs232 (ftdi232rl chip) to pc. Messages should arrive to pc with one second delay, instead they arrive with 4 second delay. and the baud rate isn't 9600 as i setted in the firmware. it's 2400.
I understood there is someting wrong with clock.
I'm using led blinking example with delay_ms(1000);
but the led is on for 4 seconds and off for 4 seconds.
i don't understand...
| Code: |
#include <main.h>
void main()
{
//Example blinking LED program
while(true)
{
output_low(LED);
delay_ms(DELAY);
output_high(LED);
delay_ms(DELAY);
}
} |
ans here is the.h
| Code: |
#include <18F2550.h>
#device ADC=16
#FUSES NOWDT //No Watch Dog Timer
#FUSES WDT128 //Watch Dog Timer uses 1:128 Postscale
#FUSES NOBROWNOUT //No brownout reset
#FUSES NOLVP //No low voltage prgming, B3(PIC16) or B5(PIC18) used for I/O
#FUSES NOXINST //Extended set extension and Indexed Addressing mode disabled (Legacy mode)
#use delay(internal=8000000)
#define LED PIN_B5
#define DELAY 1000
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i hope there's someone who can help me... |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Nov 03, 2014 7:20 pm |
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I was able to fix it by adding CPUDIV1 to the #fuses, but I'm not sure why
that works, because the oscillator diagram in the 18F2550 data sheet
does not show the internal oscillator going through the CPUDIV block. |
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temtronic
Joined: 01 Jul 2010
Posts: 9225
Location: Greensville,Ontario
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| Posted: Mon Nov 03, 2014 8:51 pm |
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Could be a compiler version bug where the registers used to configure he clock are wrong? or the selection of internal vs. external is wrong ?
You should post your compiler version, others may know.
it is 'strange' to say the least !
Jay |
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antosci
Joined: 29 Apr 2013
Posts: 13
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| Posted: Tue Nov 04, 2014 7:11 am |
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my version is pcwhd 5.025... and with #FUSES CPUDIV1 it all works.
but i don't understand why !
thank's a lot |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19504
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| Posted: Tue Nov 04, 2014 10:20 am |
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I agree you should not need CPUDIV1, but my guess would be that this 'accidentally' makes the compiler write to the OSCCON register.
Normally when using the internal RC, you have to manually force this with the line:
setup_oscillator(OSC_8MHZ);
at the start of your main code.
When using INT_RC mode, the oscillator speed is set in the code _after_ boot, not in the fuses. The chip defaults to waking at 1MHz (surprised it gives 4 seconds, not 8...).
I have to ask, why you are using a USB chip, with the internal oscillator?. Seems a waste of pins, since this chip cannot give USB like this. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Nov 04, 2014 10:29 pm |
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When using the INTRC_IO fuse with the 18F4550, if you add this line to
main(), then CPUDIV1 is not needed:
| Code: | | setup_oscillator(OSC_8MHZ | OSC_INTRC); |
With the line above, OSCCON is set to 0x72. Without that line, it's set to
0x70 in the startup code in main(). The only difference is in the SCS bits
which select between the internal and primary oscillator.
This makes me think that the oscillator circuit for 18F4550 is more like
the one for 18F45K50. In the 18F45K50 diagram, if you choose Primary
oscillator with the SCS bits, then the INTOSC signal is taken through the
CPUDIV circuit. If you choose Internal Oscillator, then INTOSC skips
the CPUDIV and is taken directly to the output mux. That explains what
we are seeing here.
I think the oscillator diagram of 18F4550 is incorrect. All these years. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19504
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| Posted: Wed Nov 05, 2014 4:22 am |
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Yes.
This is doubly 'confirmed' by the speed being seen. The default for the INT_RC route, is 1MHz, but if the 8MHz INT_RC is being routed to the CPUDIV divider, the default for this divider, is /4. 8MHz/4, then gives the 2Mhz being seen.
I suspect nobody has noticed, since as you have to have a crystal to use USB, it is more common to only use the RC oscillator for things like sleep operation, where a lower speed is selected.
On chips where the USB can be locked to a PLL off the incoming USB bus, so an accurate oscillator is not needed, this route is instead often used.
An interesting 'missing line' on the published circuit diagram..... |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Nov 05, 2014 3:05 pm |
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Here is a modified oscillator diagram for the 18F4550:
-----
Edit: Re-uploaded to imgur for longer preservation.
Last edited by PCM programmer on Mon Nov 19, 2018 3:06 am; edited 1 time in total |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19504
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| Posted: Thu Nov 06, 2014 1:28 am |
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I suspect the route would be directly from the line joining the 8MHz between the INTOSC postscaler, and the MUX, , not from the output of the MUX. If you look at the other chips where this line is present, it is normally from this point.
Best Wishes |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Nov 07, 2014 1:47 pm |
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I disagree. If I test it with 1 MHz or 2 MHz, or 31000 Hz, it behaves in
the same way. This means the output of the internal RC divider (mux)
is applied to the CPUDIV block. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19504
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| Posted: Sun Nov 09, 2014 5:09 am |
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If it 'behaves the same way', then it must come from before the Mux.
If it changes, then it'd come from after.
Best Wishes |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Nov 09, 2014 10:35 am |
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| Quote: |
I suspect the route would be directly from the line joining the 8MHz
between the INTOSC postscaler, and the MUX, not from the output of the
MUX. If you look at the other chips where this line is present, it is
normally from this point.
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Can you post the name of a PIC that has this in the data sheet ?
Where only 8 MHz goes into CPUDIV ? |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19504
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| Posted: Sun Nov 09, 2014 3:38 pm |
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| Look for instance at the 46J50. The internal 8MHz oscillator is taken before the MUX, and this or the primary oscillator can be selected to feed CPUDIV. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Nov 09, 2014 5:21 pm |
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| OK, I see what you mean now. I modeled my diagram off the 18F45K50. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19504
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| Posted: Mon Nov 10, 2014 1:14 am |
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There seem to be three variants:
1) Takes one branch before the MUX (46J50)
2) Takes multiple branches before the MUX (4620)
3) Takes the output of the MUX (45K50)
Only a sequential test of the speeds achieved with all the combinations, would 'prove' which the chip has.
In my memory, I've seen far more chips doing '1' or '2', than '3'. May be wrong, but I think that is the case. |
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