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rhaguiuda
Joined: 05 Sep 2007
Posts: 46
Location: Londrina - Brazil
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| Problem Migrating to 18F4620 from 18F458 |
 Posted: Fri Jul 04, 2008 11:25 am |
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Hi.
I have a big program (greater than 3000 lines of code) which was first created for 18F458 and works perfectly. It's a code for a weighting scale.
Now, I'm trying to migrate a 18F4620 with exactly the same code but the system doesn't work as expected.
When using the 18F458, the ADC results vary from 6000 to 50000 (correct and expected values). With 18F4620 the ADC results goes from 50 to 350 and sometimes the program freezes.
The PIC is interfaced to a TC520 from Microchip using 7 digital I/O pins.
I'v tried to disable almost everything in code and keep only the ADC initialization routine and ADC read routine, but didn't work.
My fuses config are:
| Code: |
#fuses HS, NOWDT, NOPROTECT, NOLVP, NOPUT, NOBROWNOUT
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Using a 8MHz crystal (without PLL).
What can be the problem? Is there any kind of fuse that I have to set or unset?
Any help will be gratefull.
Thanks!!! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jul 04, 2008 11:27 am |
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| Post the compiler versions used for the first PIC, and for the 2nd PIC. |
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rhaguiuda
Joined: 05 Sep 2007
Posts: 46
Location: Londrina - Brazil
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| Posted: Fri Jul 04, 2008 11:37 am |
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Sorry!!!
Compiler for both PICs: 4.017 PCH |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jul 04, 2008 11:53 am |
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Use the following test program for the 18F548:
| Code: |
#include <18F458.h>
#device adc=10
#fuses HS,NOWDT,NOPROTECT,BROWNOUT,PUT,NOLVP
#use delay(clock=8000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
//=================================
void main()
{
int16 result;
setup_adc_ports(AN0);
setup_adc(ADC_CLOCK_DIV_16); // For 8 MHz osc
set_adc_channel(0);
delay_us(15);
while(1)
{
result = read_adc();
printf("%LX ", result);
delay_ms(500);
}
} |
For the 18F4620, use the same program except change the ADC divisor
to this:
| Code: | | setup_adc(ADC_CLOCK_DIV_8); // For 8 MHz osc |
Post the results of the tests. (This assumes you're using ADC channel 0). |
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rhaguiuda
Joined: 05 Sep 2007
Posts: 46
Location: Londrina - Brazil
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| Posted: Fri Jul 04, 2008 12:00 pm |
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Thanks for all help PCM Programmer
Sorry, I didn't explained well. I'm not using the PIC internal ADC, I'm using an external ADC (TC520 with TC500 both from Microchip).
Anything else that can be done? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jul 04, 2008 12:21 pm |
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OK, I skipped over checking out the TC500 that you mentioned.
This is a 17-bit A/D. You didn't say what your input range is, but
with a 0 to 5v input, that's 38 uV per step. That's an incredibly low
level for a PIC circuit. It would require very, very careful PCB layout.
Did you build the board, or did you buy it ? If you bought it, post the
manufacturer and part number of the board.
Are you using the same board for these tests ? i.e., did you pull out
the 18F458 from a socket and substitute the 18F4620 ? |
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rhaguiuda
Joined: 05 Sep 2007
Posts: 46
Location: Londrina - Brazil
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| Posted: Fri Jul 04, 2008 12:40 pm |
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PCM,
I'm using a 1V input range from a Load Cell Sensor. (7.62uV per step).
I've built the PCB. It's layout has been designed with lots of caution (including By-pass capacitors on all ICs, analod and digital grould planes and high speed circuitry away from low speed analog circuitry).
The basic schematic is: load cell sends signal to a instrumentation amplifier (AD620 from Analog Devices). It's gain is set to 120. Then this amplified signal is injected into the TC500 (17bit AD from Microchip). The TC520 is a serial adapter interface for TC500AD since TC500 does not have a serial interface for interfacing microcontrollers.
Anyway, I'm using the same board with both PICs. I did pull out the 18F458 from a socket and subtituite the 18F4620.
I have no idea or explannation on why the ADC changes its values so raddicaly....
P.S. Sorry about my english if anything is wrong or make no sense. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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rhaguiuda
Joined: 05 Sep 2007
Posts: 46
Location: Londrina - Brazil
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| Posted: Sat Jul 05, 2008 2:10 pm |
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Thanks PCM for your help.
I've adjusted the LOAD VALUE of TC520 and for now it's working, but a little different when the 18F458 was in place. |
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