Post by thread:[PIC]: Re: Do I need pull-up resistors on PortA

Tim, Disregard my previous email. I was thinking of RA4 which is open drain. RA2 ids the VREF- pin when using AD converters. This pin might power up in analog mode. Have you changed porta to digital I/O? This may be the problem. {Quote hidden}> Looking in the 16F877 Data Sheet, I don't see any internal pull-up > resistors on any ports except port B has a weak pull-up. > > Does this mean that I have to add external pull-up resistors to get +5V > on Port A pins? > > When I connect my scope to PortA,2 which should show a pulse signal, I > see the signal resting at Gnd. > When I add a 2.2k Ohm resistor from PortA,2 to Vcc, I see my +5V to Gnd > swing. > > This is disturbing... > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

This is my configuration... did I miss something for port A? bcf STATUS, RP0 ; select bank 0 clrf PORTA ; clear PORTA clrf PORTB ; clear PORTB clrf PORTC ; clear PORTC clrf PORTD ; clear PORTD clrf PORTE ; clear PORTE bsf STATUS, RP0 ; select bank 1 clrf TRISA ; set PORTA as output clrf TRISB clrf TRISC clrf TRISD clrf TRISE movlw b'00000111' movwf ADCON1 ; PORTA inputs = digital {Original Message removed}

No, I don't believe you forgot anything. This looks good to me. Just make sure you go back to bank 0 before you write anything to the port or otherwise you'll write to the TRIS register and select some A/D combination, but I'm guessing that you are doing that below what is shown here. The only other possibility that I can think of is that you have a bad part. You might want to try another '877' part. Regards, Jim {Quote hidden}> This is my configuration... did I miss something for port A? > > > bcf STATUS, RP0 ; select bank 0 > > clrf PORTA ; clear PORTA > clrf PORTB ; clear PORTB > clrf PORTC ; clear PORTC > clrf PORTD ; clear PORTD > clrf PORTE ; clear PORTE > > bsf STATUS, RP0 ; select bank 1 > > clrf TRISA ; set PORTA as output > clrf TRISB > clrf TRISC > clrf TRISD > clrf TRISE > > movlw b'00000111' > movwf ADCON1 ; PORTA inputs = digital > > > > > {Original Message removed}

On Tue, 29 Jan 2002, James Paul wrote: > No, I don't believe you forgot anything. This looks good to me. > Just make sure you go back to bank 0 before you write anything > to the port or otherwise you'll write to the TRIS register and > select some A/D combination, but I'm guessing that you are doing > that below what is shown here. You know, that would explain it. If the PORTA data register is all zeros from the CLRF and the TRIS register bit is toggled instead of the PORTA data bit, you'd go from a LOW output to a float... which a pullup resistor would make look ike a HIGH output. So on a 'scope it would look like a square wave, but be 180 degrees out of phase with what he thinks the code is doing. I'll have to remember to use an asymmetrical pattern if I ever try to troubleshoot something like this with a scope. Dale -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Tim, Glad to help. I wish you the best of luck in the rest of you code development efforts. And remember, this list is always here if you need any further assistance. Thanks and Regards, Jim ----- Original Message ----- From: WEBB,TIM (A-Sonoma,ex1) <spam_OUTtim_webbTakeThisOuTAGILENT.COM> To: <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> Sent: Tuesday, January 29, 2002 3:22 PM Subject: Re: [PIC]: Re: Do I need pull-up resistors on PortA of a 16F877 {Quote hidden}> That was it... > > I need to go back to bank 0. > > Problem resolved. > > Add this one to the Pic's for Dummies book > > Thanks, > > Tim > > > > {Original Message removed}