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Danny.
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| Pic16f877A, sporadic working. |
 Posted: Fri Apr 21, 2006 6:16 am |
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This is a continuation of a post I made yesterday, but the simple mistake that I made was fixed by suggestions from another poster, so I thought I'd try throwing another question to the community...
I have a PIC16f877A wired to a serial port, (RC6) pin25
Attached to the chip i have,
1 8MHz crystal, connected to a ground through two 22pf capacitors, (arranged like they are in the 16f877 manual.
power connected to both vdd and vss pins, (does anyone know if both of the power supplies *need* to be connected, or are they connected internaly,
I also have a LED (with 4.7K series resistor), on RB0 (annode to VDD cathode to RB0)
my voltage source I'm rtying to measure is on RA0 (pin 2)
and it's all powered by an ATX supply from a computer, (so I can't see that there are supply problems)
| Code: | #include <16f877.h>
#device adc=10
#fuses HS,NOPROTECT,NOWDT,NOBROWNOUT,NOLVP
#use delay(clock=8000000)
#use rs232(baud=9600,parity=N,xmit=PIN_C6,bits=8, INVERT)
unsigned char j;
void main(void)
{
int16 result;
set_tris_a(0xFF);
setup_adc_ports(0);
setup_adc(ADC_CLOCK_DIV_8);
set_adc_channel(0);
while(1)
{
output_high(PIN_B0);
result = read_adc();
printf("voltage is: %lx\n\r", result);
delay_ms(500);
output_low(pin_B0);
delay_ms(500);
}
} |
The problem is that it only seems to work when it wants to.
that is to say, it won't necessarily work when it's first powered up, but will the spring into life (returning reasonable data to the terminal), the just as suddenly stop again, (no lights no data)...
I've looked and searched and googled, and can't seem to find anything remotly like the problem that I'm having.
Does anyone have any ideas? |
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rberek
Joined: 10 Jan 2005
Posts: 207
Location: Ottawa, Canada
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| Posted: Fri Apr 21, 2006 7:05 am |
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Which output from the ATX power supply are you using? How is it hooked to the board. Which RS232 transceiver are you using?
Can you show us a schematic? |
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Charlie U
Joined: 09 Sep 2003
Posts: 183
Location: Somewhere under water in the Great Lakes
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| Posted: Fri Apr 21, 2006 7:08 am |
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First, I'd add PUT to the fuses. This is the power up timer that delays the internal reset until (in theory) the crystal oscillator has fully started. This should not help the intermittent problem, but should be done anyway.
Next, how is your MCLR pin connected? This sounds like your MCLR pin is not connected properly or may be loose. |
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Guest
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| Posted: Fri Apr 21, 2006 7:39 am |
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thanks to you both!!
the problem was that the MCLR pin was not connected, (and floats high?).
Now it's all connected and working, so thats great, thanks guys!!
The atx power supply...?
I've long jumper leads from my breadboard pushed into the pins of the floppy connector (+5 red and 0 black), and a paperclip shorting pins 14 and 15 (green and black) on the main socket to make it constantly on... (I will re house this eventually but it works for now...) |
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