Post by thread:[PIC][EE]: Unstable circuit

Hi!! I have a PIC16F877 circuit and im having big problems to get it stable. Problem: It will only run for a short time and only if im touching GND with one hand. When I touch GND with one hand all I have to do is wave the other hand a few inces from the circuit to get it to reset, now if I keep that hand really still I can watch it run for like 5-10 secs before it lock ups (not resets). Hardware: All I have is a 4Mhz 16f877, osc caps are 27p One LED on RC4 with a resistor to GND. Max232 with all the caps on RC6 and 7. The other end of the max232 is connected to my com1. A reset button with a 10k pullup resistor. All my cables are short and nicely layedout and my powersupply delivers a stable +5v. What I have tried so far: I have tried to put +5 on either and both of the VDD pins, same thing with the VSS. I have put caps between none, either or both of the VSS/VDD pins. I disconnected the Max232 on rc6 and rc7, still the same problem. I tried a 16f874 at both 20 and 4Mhz, same thing. Help me! /Fredrik -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

I start my code with this (got it of the net somewhere). movlw b'00000000' ; all port pins = low movwf PORTA movlw b'00000000' movwf PORTB movlw b'00000000' movwf PORTC movlw b'00000000' movwf PORTD movlw b'00000000' movwf PORTE bsf STATUS,RP0 ; set RAM Page 1 for TRIS registers movlw b'00000000' ; all IO pins = outputs movwf TRISA movlw b'00000000' movwf TRISB movlw b'00000000' movwf TRISC movlw b'00000000' movwf TRISD movlw b'00000000' movwf TRISE movlw b'00000110' ; all analog pins = digital movwf ADCON1 bcf STATUS,RP0 ; back to RAM page 0 /Fredrik {Original Message removed}

You don't mention -mclr Pull it up to Vdd with a 4k7 resistor Mike ----- Original Message ----- From: "Fredrik Axtelius" <.....fredrik.axteliusKILLspam@spam@TELIA.COM> To: <PICLISTKILLspamMITVMA.MIT.EDU> Sent: Monday, August 05, 2002 11:59 PM Subject: [PIC][EE]: Unstable circuit > Hi!! > > I have a PIC16F877 circuit and im having big problems to get it stable. > > Problem: > It will only run for a short time and only if im touching GND with one hand. > When I touch GND with one hand all I have to do is wave the other hand a few inces from the circuit to get it to reset, now if I keep that hand really still I can watch it run for like 5-10 secs before it lock ups (not resets). > > Hardware: > All I have is a 4Mhz 16f877, osc caps are 27p > One LED on RC4 with a resistor to GND. > Max232 with all the caps on RC6 and 7. The other end of the max232 is connected to my com1. > A reset button with a 10k pullup resistor. > All my cables are short and nicely layedout and my powersupply delivers a stable +5v. > > What I have tried so far: > I have tried to put +5 on either and both of the VDD pins, same thing with the VSS. {Quote hidden}> I have put caps between none, either or both of the VSS/VDD pins. > I disconnected the Max232 on rc6 and rc7, still the same problem. > I tried a 16f874 at both 20 and 4Mhz, same thing. > > Help me! > /Fredrik > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Yes, of course it's a typo :) I have both Vdd to +5 and both Vss to GND. /MCLR is pulled up with a 10k resistor (also tried 1k). Still having exactly the same problems. Any more ideas? /frax ----- Original Message ----- From: "Derek Cowburn" <.....derekKILLspam.....COWBURN.US> To: <EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU> Sent: Tuesday, August 06, 2002 4:53 PM Subject: Re: [PIC][EE]: Unstable circuit {Quote hidden}> > > I have tried to put +5 on either and both of the VDD pins, > > same thing with > > the VSS. > > +5 to both Vdd. Vss to Ground (not +5). Typo? > > I had a similar problem and it was the /MCLR was not pulled high like Mike > indicates below. Same "touch it and it resets" effect. > > -Derek > > > > {Original Message removed}

HI, ADD 0.1uF on MCRL and GND (Recommend By Microchip), and 0.1uF on Each VCC Pin. 5 / \ 10K / \ ----------MCRL | | -- -- 0.1uF | | GND Denis ----- Original Message ----- From: "Fredrik Axtelius" <fredrik.axteliusspam_OUTTELIA.COM> To: <@spam@PICLISTKILLspamMITVMA.MIT.EDU> Sent: Tuesday, August 06, 2002 3:35 PM Subject: Re: [PIC][EE]: Unstable circuit Yes, of course it's a typo :) I have both Vdd to +5 and both Vss to GND. /MCLR is pulled up with a 10k resistor (also tried 1k). Still having exactly the same problems. Any more ideas? /frax ----- Original Message ----- From: "Derek Cowburn" <KILLspamderekKILLspamCOWBURN.US> To: <RemoveMEPICLISTTakeThisOuTMITVMA.MIT.EDU> Sent: Tuesday, August 06, 2002 4:53 PM Subject: Re: [PIC][EE]: Unstable circuit {Quote hidden}> > > I have tried to put +5 on either and both of the VDD pins, > > same thing with > > the VSS. > > +5 to both Vdd. Vss to Ground (not +5). Typo? > > I had a similar problem and it was the /MCLR was not pulled high like Mike > indicates below. Same "touch it and it resets" effect. > > -Derek > > > > {Original Message removed}

Tried that, still having the same problems... /frax ----- Original Message ----- From: "Denis Seguin" <spamBeGonedenisspamBeGonecitenet.net> To: <TakeThisOuTPICLISTEraseMEspam_OUTMITVMA.MIT.EDU> Sent: Tuesday, August 06, 2002 9:55 PM Subject: Re: [PIC][EE]: Unstable circuit {Quote hidden}> HI, > > ADD 0.1uF on MCRL and GND (Recommend By Microchip), and 0.1uF on Each VCC > Pin. > > 5 > / > \ 10K > / > \ > ----------MCRL > | > | > -- > -- 0.1uF > | > | > GND > > > > Denis > > > ----- Original Message ----- > From: "Fredrik Axtelius" <RemoveMEfredrik.axteliusTakeThisOuTTELIA.COM> > To: <PICLISTEraseME.....MITVMA.MIT.EDU> > Sent: Tuesday, August 06, 2002 3:35 PM > Subject: Re: [PIC][EE]: Unstable circuit > > > Yes, of course it's a typo :) > I have both Vdd to +5 and both Vss to GND. > /MCLR is pulled up with a 10k resistor (also tried 1k). > > Still having exactly the same problems. > > Any more ideas? > > /frax > > ----- Original Message ----- > From: "Derek Cowburn" <EraseMEderekCOWBURN.US> > To: <RemoveMEPICLISTEraseMEEraseMEMITVMA.MIT.EDU> > Sent: Tuesday, August 06, 2002 4:53 PM > Subject: Re: [PIC][EE]: Unstable circuit > > > > > > I have tried to put +5 on either and both of the VDD pins, > > > same thing with > > > the VSS. > > > > +5 to both Vdd. Vss to Ground (not +5). Typo? > > > > I had a similar problem and it was the /MCLR was not pulled high like Mike > > indicates below. Same "touch it and it resets" effect. > > > > -Derek > > > > > > > {Original Message removed}

Fredrik Axtelius wrote: > > Hi!! > > I have a PIC16F877 circuit and im having big problems to get it stable. Disable WDT Disable LVP Check crystal circuit, Vss connection to it, keep it compact and near the chip Wrong OSC fuse setting, try HS mode Floating inputs Disconnect PC from circuit Tie MCLR hard to 5V Verify software Delete all software except for "flashy LED" Check ground rails in circuit Connect BOTH Vdd and Vss to power supply Use another 877 chip Verify programming Change power supplies Check circuit for dry joints & shorted IO pins Try LED on another IO pin Check for BSF instructions on PORTS Give me $10, that helps Try this, it works.. list p=16f877 ; processor type #include "p16f877.inc" ; ; ------------------ ; CONFIGURATION FUSE ; ------------------ ; __CONFIG _CP_OFF & _WRT_ENABLE_OFF & _HS_OSC & _WDT_OFF & _PWRTE_OFF & _BODEN_OFF & _LVP_OFF & _CPD_OFF & _DEBUG_OFF ; ; The purpose of this program is to make a LED turn on and off ; The LED is connected to PortB any pin ; The flash rate is 500mS @ 4MHz ; CBLOCK 0x20 DelayL ; delay register LOW byte DelayM ; delay register MID byte DelayH ; delay register HIGH byte ENDC ; ; ------------- ; PROGRAM START ; ------------- ; org 0h ; startup address = 0000 clrf PORTA clrf PORTB clrf PORTC clrf PORTD clrf PORTE bsf Status,RP0 ; set RP0 for RAM page 1 clrf TrisA ; all PortA = outputs clrf TrisB ; all PortB = outputs clrf TrisC ; all PortC = outputs clrf TrisD ; all PortD = outputs clrf TrisE ; all PortE = outputs ; ; ------------------------- ; SET ANALOG/DIGITAL INPUTS ; ------------------------- ; movlw b'00000110' ; all digital movwf ADCON1 bcf Status,RP0 ; set RP0 for RAM page 0 start clrf PORTB call Delay500 ; execute a 500mS delay movlw 0xFF movwf PORTB call Delay500 ; execute a 500mS delay goto start ; do this loop forever ; ; --------------------------------------- ; SUBROUTINE: waste time for 500mS @ 4MHz ; --------------------------------------- ; Delay500 clrf DelayL ; clear DelayL to 0 clrf DelayM ; clear DelayM to 0 movlw 3h ; set DelayH to 3 movwf DelayH Wait1 decfsz DelayL ; subtract 1 from DelayL goto Wait1 ; if not 0, goto Wait1 decfsz DelayM ; subtract 1 from DelayM goto Wait1 ; if not 0, goto Wait1 decfsz DelayH ; subtract 1 from DelayH goto Wait1 ; if not 0, goto Wait1 return ; finished the delay end -- Best regards Tony mICros http://www.bubblesoftonline.com RemoveMEsalesspam_OUTKILLspambubblesoftonline.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

{Quote hidden}> -----Original Message----- > From: Fredrik Axtelius [SMTP:RemoveMEfredrik.axteliusTakeThisOuTspamTELIA.COM] > Sent: Tuesday, August 06, 2002 12:00 AM > To: EraseMEPICLISTspamspamBeGoneMITVMA.MIT.EDU > Subject: [PIC][EE]: Unstable circuit > > Hi!! > > I have a PIC16F877 circuit and im having big problems to get it stable. > > Problem: > It will only run for a short time and only if im touching GND with one > hand. > When I touch GND with one hand all I have to do is wave the other hand a > few inces from the circuit to get it to reset, now if I keep that hand > really still I can watch it run for like 5-10 secs before it lock ups (not > resets). > > Hardware: > All I have is a 4Mhz 16f877, osc caps are 27p > One LED on RC4 with a resistor to GND. > Max232 with all the caps on RC6 and 7. The other end of the max232 is > connected to my com1. > A reset button with a 10k pullup resistor. > All my cables are short and nicely layedout and my powersupply delivers a > stable +5v. > > What I have tried so far: > I have tried to put +5 on either and both of the VDD pins, same thing with > the VSS. > I have put caps between none, either or both of the VSS/VDD pins. > I disconnected the Max232 on rc6 and rc7, still the same problem. > I tried a 16f874 at both 20 and 4Mhz, same thing. > > Help me! > /Fredrik > You need to make sure that MCLR is tied to Vdd with a (e.g. 10k) resistor, and also make sure that RB3 (PGM) is pulled low via another resistor if you have low voltage programming enabled. Regards Mike -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Fredrik Axtelius wrote: > > We have a winner!! > Thanks alot, RB3->GND solved everything, it now runs just great!! > Can someone explain why? > > To Tony Nixon: I tried all the thing you suggested and was just about to send you the $10. Now that Michaels tip worked do I still need to send you the money, if yes then I need your address :) One of the things I mentioned was to check that LVP was disabled. You will also notice this in the __CONFIG directive in the code I posted. Grounding the LVP input suggests that you left LVP = ON. When LVP mode is active and LVP is high or floating, the chip tries to enter low voltage programing mode. See the link below for credit card transactions. Just kidding :-) Glad it's working -- Best regards Tony mICros http://www.bubblesoftonline.com RemoveMEsalesKILLspambubblesoftonline.com -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.