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pic16f84a stops running HELP!!!!

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teslacoolguy

Thu Nov 29 2007, 07:33PM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

this is my first pic project so i built a simple program that blinks a bunch of led's connected with bc550 transistors. RA0-RA3 are connected to led's that each go to one letter of my cousin Joey but in led's(see picture)and RB0-RB5 are connected directly to 6 low power ultrabright blue led's(one on each port)that i made flash around the border of my name. The oscillattor is a 10mhz resonater. when i got it all together and powered it up it worked like a charm for about 2-3 seconds and than stopped. i realised after a bunch of poking around that when i touch MCLR and RA4 with my finger it started to work again but after a couple of seconds it stopped. I am really puzzeled so if anyone has any tips plz let me know. Here is the program that works fine on my dev board when using 1 led for each letter and the led's on portB are steady and not flashing(same as in the real thing) the code is in basic

main:
TRISA = 0
TRISB = 0
PORTA = %00000001
PORTB = %00111111
delay_ms(300)
PORTA = %00000011
delay_ms(300)
PORTA = %00000111
delay_ms(300)
PORTA = %00001111
delay_ms(300)
PORTA = %00000000
delay_ms(200)
PORTA = %00001111
delay_ms(200)
PORTA = %00000000
delay_ms(200)
PORTA = %00001111
delay_ms(200)
PORTA = %00000000
delay_ms(200)
PORTA = %00001111
delay_ms(200)
PORTA = %00000000
delay_ms(200)
PORTA = %00001111
delay_ms(200)
PORTA = %00000000
delay_ms(200)
PORTA = %00001111
delay_ms(300)
PORTA = %00001110
delay_ms(300)
PORTA = %00001100
delay_ms(300)
PORTA = %00001000
delay_ms(300)
PORTA = %00000000
delay_ms(300)
goto main
end.

Bjørn

Thu Nov 29 2007, 08:27PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

It looks a bit like you forgot to ground your reset pin, if that is true it would cause such problems.

uzzors2k

Thu Nov 29 2007, 09:35PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

I thought you had to pull the reset/MCLR pin high?

Bjørn

Thu Nov 29 2007, 10:54PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

You are correct, it should be pulled high. It is an active low input.

Usually connecting it directly to VDD in simple circuits like this is fine, but there are some cases where it will not be good enough. Using a resistor fixes most problems but in some cases a delay circuit must be made to make sure the PSU and oscillator is stable before the chip comes out of reset to make sure it does not lock up.

Ken M.

Fri Nov 30 2007, 03:07AM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

If fidgeted with pics before and most have an internal reset system, as for the code...................If ur using basic ur Delay should be "pause X" where pause is the # of milliseconds u want it to pause for. If not just listen to bjorn, he's more informed then I am, also I haven't messed with pics in 2 years...

Conundrum

Fri Nov 30 2007, 08:14AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

Also MCLR is vulnerable to ESD, be very careful! i've had this problem and it can cause random lockups.
the fix is to put a 15v zener across this pin if using the chip in an ICSP or other application.

btw this also applies to 12xxx chips.
regards, -A

Steve Conner

Fri Nov 30 2007, 10:13AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yep, looks like you forgot the pull-up resistor on MCLR.

uzzors2k

Fri Nov 30 2007, 12:12PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

WhiteArc wrote ...

If fidgeted with pics before and most have an internal reset system, as for the code...................If ur using basic ur Delay should be "pause X" where pause is the # of milliseconds u want it to pause for. If not just listen to bjorn, he's more informed then I am, also I haven't messed with pics in 2 years...

It looks like Mikrobasic to me, in which case his syntax is ok.

Capper

Fri Nov 30 2007, 12:32PM

Registered Member #914 Joined: Fri Jul 20 2007, 06:22PM
Location: South Bend, IN
Posts: 85

Did you disable the watchdog timer? Look at your configuration bits. That was one of my first problems working with PICs.

teslacoolguy

Tue Dec 04 2007, 05:32AM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

problem fixed i dident connect MCLR to the 5v line

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