Post by thread:[PIC]: weird I/O problem

Heips, I am using a PIC16F877 and am stuck with a strange problem, which I hope is due to a mistake on my part rather than a broken PIC. Summary: bsf STATUS, RP0 ; Use register bank number 1 movlw b'10000110' ; Set port A as digital I/O movwf ADCON1 ; instead of ADC movlw b'00000000' ; All pins set to output movwf TRISA ; on port A movlw H'FF' ; Assert all pins movwf PORTA ; on port A I upload it to the chip using a bootloader and serial connection, and reset the circuit. All pins on port A now measure 5.00 volts between them and GND, EXCEPT for pin 4 (RA4/T0CKL), which measures something between 0.8 and 3.3 volts. Usually I would blame this on a connection problem somewhere, but now I am using a breadboard and the pin in question is not connected to anything (neither are the other port A pins). Maybe it has something to do with the timer associated with that pin? I have tried some different configurations, and each one got a different voltage, but never the normal +5V. What do I need to do (starting with the default startup configuration) in this case, using the PIC16F877 @ 4 MHz with a crystal oscillator using the following config word: _CP_OFF _WDT_OFF _BODEN_ON _PWRTE_ON _XT_OSC _WRT_ENABLE_ON _LVP_OFF _DEBUG_OFF _CPD_OFF Hope the chip is ok :-) Thanks for any pointers, Kinds regards Dennis Noordsij -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

Sorry for the follow-up Does it sound like an obvious case of floating-pin-syndrome? I haven't yet made sure all pins are going somewhere (testing incrementally is easier this way), but is it still strange only pin RA4 has this problem? In a faraway galaxy, Dennis Noordsij wrote on Sunday 14 October 2001 00:50 : {Quote hidden}> Heips, > > I am using a PIC16F877 and am stuck with a strange problem, which I hope is > due to a mistake on my part rather than a broken PIC. > > Summary: > > bsf STATUS, RP0 ; Use register bank number 1 > > movlw b'10000110' ; Set port A as digital I/O > movwf ADCON1 ; instead of ADC > > movlw b'00000000' ; All pins set to output > movwf TRISA ; on port A > > movlw H'FF' ; Assert all pins > movwf PORTA ; on port A > > I upload it to the chip using a bootloader and serial connection, and reset > the circuit. > > All pins on port A now measure 5.00 volts between them and GND, EXCEPT for > pin 4 (RA4/T0CKL), which measures something between 0.8 and 3.3 volts. > > Usually I would blame this on a connection problem somewhere, but now I am > using a breadboard and the pin in question is not connected to anything > (neither are the other port A pins). > > Maybe it has something to do with the timer associated with that pin? I > have tried some different configurations, and each one got a different > voltage, but never the normal +5V. > > What do I need to do (starting with the default startup configuration) in > this case, using the PIC16F877 @ 4 MHz with a crystal oscillator using the > following config word: > _CP_OFF > _WDT_OFF > _BODEN_ON > _PWRTE_ON > _XT_OSC > _WRT_ENABLE_ON > _LVP_OFF > _DEBUG_OFF > _CPD_OFF > > Hope the chip is ok :-) > Thanks for any pointers, > Kinds regards > Dennis Noordsij -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu

On Saturday 13 October 2001 02:50 pm, Dennis Noordsij wrote: > All pins on port A now measure 5.00 volts between them and GND, EXCEPT for > pin 4 (RA4/T0CKL), which measures something between 0.8 and 3.3 volts. > > Usually I would blame this on a connection problem somewhere, but now I am > using a breadboard and the pin in question is not connected to anything > (neither are the other port A pins). As described in the data sheet, this pin has an open drain output, and would require a pullup resistor if you need a high voltage (though it could sink current fine by itself). -- Ned Konz currently: Stanwood, WA email: nedKILLspambike-nomad.com homepage: http://bike-nomad.com -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam.....mitvma.mit.edu

I might be totally wrong here, but here's my off the top of my head, no paperwork in front of me, semiguessing response. First, your summary didn't show you switching back to bank 0. I am pretty sure the porta register is in bank 0. Second, I think pin 4 might be open collector. I think this would mean that it can sink but not source current. I could be wrong though. Best bet is to check the datasheet at http://www.microchip.com. Hope this helps, Josh Koffman Dennis Noordsij wrote: {Quote hidden}> > Heips, > > I am using a PIC16F877 and am stuck with a strange problem, which I hope is > due to a mistake on my part rather than a broken PIC. > > Summary: > > bsf STATUS, RP0 ; Use register bank number 1 > > movlw b'10000110' ; Set port A as digital I/O > movwf ADCON1 ; instead of ADC > > movlw b'00000000' ; All pins set to output > movwf TRISA ; on port A > > movlw H'FF' ; Assert all pins > movwf PORTA ; on port A > > I upload it to the chip using a bootloader and serial connection, and reset > the circuit. > > All pins on port A now measure 5.00 volts between them and GND, EXCEPT for > pin 4 (RA4/T0CKL), which measures something between 0.8 and 3.3 volts. > > Usually I would blame this on a connection problem somewhere, but now I am > using a breadboard and the pin in question is not connected to anything > (neither are the other port A pins). > > Maybe it has something to do with the timer associated with that pin? I have > tried some different configurations, and each one got a different voltage, > but never the normal +5V. > > What do I need to do (starting with the default startup configuration) in > this case, using the PIC16F877 @ 4 MHz with a crystal oscillator using the > following config word: > _CP_OFF > _WDT_OFF > _BODEN_ON > _PWRTE_ON > _XT_OSC > _WRT_ENABLE_ON > _LVP_OFF > _DEBUG_OFF > _CPD_OFF > > Hope the chip is ok :-) > Thanks for any pointers, > Kinds regards > Dennis Noordsij > > -- > http://www.piclist.com hint: To leave the PICList > EraseMEpiclist-unsubscribe-requestspam_OUTTakeThisOuTmitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestspam_OUTmitvma.mit.edu

On Sunday 14 October 2001 01:13, you wrote: > Hi Dennis! > > I'm not sure but I believe RA4 is an open colector output, so you need > some sort of pull up resistor. > > Regards > Hamilton Horta > Hi, I am just not too familiar with the open-collector open-drain etc concepts, the explanation on piclist.com is also a bit cryptic (for me anyway :) I put a 10k resister between RA4 and VDD, and now everything works as expected :-) Does anyone have a pointer to somewhere I can learn a little more about these concepts? My background is programming (which is why I got interested in the PIC's) and not electronics (which I am learning as I go whenever I want the PIC to do something new :-) Thanks again for the quick and great replies, this list is truly a great source of information. Thanks again Dennis -- http://www.piclist.com hint: To leave the PICList @spam@piclist-unsubscribe-requestKILLspammitvma.mit.edu

Hi all, Back out of hospital and just living till the next operation :o( Ok Dennis, I have not got any online examples at hand, but I can describe it easily. I assume that you are familiar with the totem poles of the North American Indians (IIRC) where they carved heads in to the pole one on top of the other. Now just look at a pair of heads, Imagine each head is a Transistor or FET, The top Transistor / FET is tied to Vdd (+5V), and the bottom one is tied to Vss (0V).the space between the two heads (transistors / FETs) is where we take our output. Inside the chip behind out totem pole is some logic to provide the signal for the output, but also a complimentary (inverted) signal, the normal signal goes to the top device (Transistor / FET) and the complimenty signal goes to the bottom device. A few parts (resistors, diodes etc) are used to make sure that while the voltage changes that BOTH devices are not switched on as that would short the +5v to 0V. When the true signal is a logic 1 (+5V) the out put will be ~+5V (due to losses in the junctions of the transistor), and the bottom device will be switched off. Now if the true signal is 0 the top device is off and the bottom device is on , causing the output to be pulled low (0V). As you can see a fair few parts are needed to drive the top device, compliment the logic, and provide a dead crossover region. It soon became clear when mixing logic devices, that a totem pole output was no good, as maybe you needed more than +5V to signal logic high, A cmos device for example may need 10V but our poor Pic sitting on +5V (and no we can not give him more voltage in) can not drive the cmos pin to a logic 1 (we would only see 0V and an undefined voltage, both could possibly be interpreted as a logic 0) To over come the above problem open collector was designed, Instead of pulling the output High, we let it float and use an EXTERNAL pull up resistor to pull the signal to what ever level we like, all we need to watch is that we do not overload the driving pin by pulling to much current, or pushing a too higher voltage in. If you have any further questions, pleas ask :o) Regards, Kat. ____________________________________________________________________________ /"\ ASCII Ribbon Campaign | K.A.Q. Electronics \ / - NO HTML/RTF in e-mail | Software and Electronic Engineering X - NO Word docs in e-mail | Perth Western Australia / \ | Ph +61 419 923 731 ____________________________________________________________________________ {Original Message removed}

> All pins on port A now measure 5.00 volts between them and GND, EXCEPT for > pin 4 (RA4/T0CKL), which measures something between 0.8 and 3.3 volts. RA4 is open collector which means it can only pull a line DOWN, not up to 5V. You have to put a pull up resistor on it for it to function as you want, however be aware of the value, if it's to low you risk drawing to much from th PIC, if it's to high you have to be careful about read-modify-write operations on port A. TTYL -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> Does anyone have a pointer to somewhere I can learn a little more about these > concepts? My background is programming (which is why I got interested in the > PIC's) and not electronics (which I am learning as I go whenever I want the > PIC to do something new :-) There are many more subjects you'll want to read about. I suggest you buy "the art of electronics" (Horowitz & Hill). Wouter van Ooijen Van Ooijen Technische Informatica: http://www.voti.nl Jal compiler for PIC uC's: http://www.xs4all.nl/~wf/wouter/pic/jal -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> bsf STATUS, RP0 ; Use register bank number 1 Or possibly bank 3 since you didn't set RP1 > movlw b'10000110' ; Set port A as digital I/O > movwf ADCON1 ; instead of ADC > > movlw b'00000000' ; All pins set to output > movwf TRISA ; on port A > > movlw H'FF' ; Assert all pins > movwf PORTA ; on port A Note that PORTA is in bank 0. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, KILLspamolinKILLspamembedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> I am just not too familiar with the open-collector open-drain etc concepts, > the explanation on piclist.com is also a bit cryptic (for me anyway :) Open drain or open collector outputs can actively pull down but not up. Another way of looking at this is that they can sink current when programmed low, but never source any. This is fine if you are connecting a load between power and the pin, like and LED and a resistor. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, RemoveMEolinTakeThisOuTembedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

>> I am just not too familiar with the open-collector open-drain etc >concepts, >> the explanation on piclist.com is also a bit cryptic (for me anyway :) >Open drain or open collector outputs can actively pull down but not up. >Another way of looking at this is that they can sink current when programmed >low, but never source any. This is fine if you are connecting a load >between power and the pin, like and LED and a resistor. Hmmm, maybe a simpler explanation? ;o) Imagine an Open Collector or Open Drain output as a switch. One of the poles of the switch, is tied to GND. The other is avaiable to you. If you connect a resistor to +vcc and to this pin, you will measure a HIGH on this pin, but when you "activate" this pin, you'll measure a LOW in this pin. Of course, since one of the sides of the "switch" is tied to ground, you can never use a pull down on it, it will always be GND for you all ;o) ---8<---Corte aqui---8<---- Alexandre Souza spamBeGonetaitospamBeGoneterra.com.br http://planeta.terra.com.br/lazer/pinball/ ---8<---Corte aqui---8<---- -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads