Post by thread:[PIC]: 16c73 RA4 as I/O will not work

I added an external pullup resistor to it but it did not help. Looking at it on the scope in does a saw tooth wave that peaks at about 1V then a sharp drop. I formated the subject wrong. I was notified that the : is required on the subject line if I want the list to except it. Original message had the same problem. Original message as follows. I am having a very are time trying to get RA4 on a 73 to work as digital I/O. What could be the problem? Here is my snipit of code that should work but does not. I am using the Hi-Tech C compiler, 7.83 or so. My real program is much larger then this and actualy does something but I need RA4 as an I/O pin. I have tried 6 or so differnt chips and they all do the same thing. Any ideas why this does not work? void main() { char TogelBit; OPTION = 0xC7; RBPU = 1; // Disable pullups on inputs, need to have put downs on them. T0CS = 0; // RA4 is an I/O pin ADON = 0; // Turn off ADC unit ADCON1 = 7; // Set Port A pins as I/O pins // Set the ports TRISA = 0x00; PORTA = 0; TRISB = 0xFF; TRISC = 0xFF; TogelBit = 1; while(1) { RA4 = TogelBit; if(TogelBit == 1) { TogelBit = 0; } else { TogelBit = 1; } } } -- Roy Souther <spam_OUTroyTakeThisOuTsilicontao.com> 01100010 10101110 11000110 11010110 00000100 10110010 10010110 11000110 01001110 11110110 11001110 00010110 10010110 00101110 10000100 10000100 -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

Hi Roy. Here's your problem: > char TogelBit; You misspelled Toggle! ;-) Seriously, though, simplify your code on the way to a solution. Use this instead: void main() { /* initialization code */ while (1) { PORTA ^= 0x10; } } -- ______________________________________ Andrew E. Kalman, Ph.D. aekKILLspampumpkininc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

At 10:19 AM 6/29/01 -0600, Roy Souther wrote: >I added an external pullup resistor to it but it did not help. > >Looking at it on the scope in does a saw tooth wave that peaks at about 1V >then a sharp drop. What kind of freqency response to you have on your scope? Is there an optional low pass filter you can switch out? This should work, but the times "on" and "off" will probably not be equal, and if you are running at 20MHz, the times on/off will only be a microsecond or two. Best regards, =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Spehro Pefhany --"it's the network..." "The Journey is the reward" EraseMEspeffspam_OUTTakeThisOuTinterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

Spehro Pefhany wrote: > > At 10:19 AM 6/29/01 -0600, Roy Souther wrote: > >I added an external pullup resistor to it but it did not help. > > > >Looking at it on the scope in does a saw tooth wave that peaks at about 1V > >then a sharp drop. > > What kind of freqency response to you have on your scope? Is there an > optional low pass filter you can switch out? This should work, but the > times "on" and "off" will probably not be equal, and if you are running > at 20MHz, the times on/off will only be a microsecond or two. Getting 20MHz at RA4 is a bit of a feat, and with most frequencies less than than you would expect more of a square wave I bet. Supplying more info re the freq and what he is driving with the PIC pin will help quite a bit. The "sawtooth" comment seems to imply that the load is too much for the PIC pin, maybe just reducing the ohms value of the pullup resistor might do it, or examination of the capacitance of the load vs the freq etc. -Roman -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

At 03:40 AM 6/30/01 +1000, you wrote: >Getting 20MHz at RA4 is a bit of a feat, and with >most frequencies less than than you would expect more >of a square wave I bet. It will be rectangular (rather than square) because the program he wrote does not treat the two states symetrically, in general. With a 20MHz MCU clock, you'd probably get a toggle frequency in the hundreds of kHz. But Bob hit the nail on the head, the capacitive loading (of the scope probe, perhaps) combined with a too-high pullup resistor on an open-drain output will lead to exactly this sort of sawtooth behavior. If this indicates a time constant of, say, 2 microseconds, and the load capacitance is 20pF, then the pullup would be something like 100K. With a 4.7K pullup, the results should be quite different. Best regards, =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Spehro Pefhany --"it's the network..." "The Journey is the reward" KILLspamspeffKILLspaminterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

Andrew E. Kalman <spamBeGonePICLISTspamBeGonemitvma.mit.edu> wrote: > Seriously, though, simplify your code on the way to a solution. Use > this instead: > > void main() > { > /* initialization code */ > > while (1) > { > PORTA ^= 0x10; > } > } Andrew: Personally, I think that's a bad suggestion. Explicitly writing 1's and 0's, as Roy originally did, ensures that he's not having a read-mofdify-write problem... Which he WOULD have had if he used your code with his original hardware (i.e., without a pullup on RA4). Without that pullup, RA4 would always read low, so your code would just repeatedly write a 1 to the pin. With a too-weak pullup, your code would have the somewhat-interesting effect of auto-adapting his toggle frequency to the time-constant of his resistor... But that probably isn't what he wanted, and it would likely confuse him to see a very asymmetrical waveform with a frequency much lower than he expected. -Andy === Andrew Warren --- TakeThisOuTaiwEraseMEspam_OUTcypress.com === IPD Systems Engineering, CYSD === Cypress Semiconductor Corporation === === Opinions expressed above do not === necessarily represent those of === Cypress Semiconductor Corporation -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

Andy Warren notes: >Explicitly writing 1's and 0's, as Roy originally did, ensures that >he's not having a read-mofdify-write problem... Which he WOULD have >had if he used your code with his original hardware (i.e., without a >pullup on RA4). etc. All true -- I had not noticed that he was running at 20MHz, and at those speeds the pin behavior of the PIC, coupled with RMW, becomes an issue. In that case, better to do while (1) { imagePORTA ^= 0x40; PORTA = imagePORTA; } As an aside, though, does this code avoid the RMW issues? while (1) { PORTA |= 0x40; PORTA &= ~0x40; } Note that the HI-TECH compiler will use bcf and bsf instructions (just two instructions total in the loop), and so I don't see how the RMW issue crops up _with_respect_to_the_port_pin_in_question (PORTA[4])_. Other pins on the port may not behave as one expects ... Regards, -- ______________________________________ Andrew E. Kalman, Ph.D. aekEraseME.....pumpkininc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservmitvma.mit.edu with SET PICList DIGEST in the body

Andy Warren wrote: >Explicitly writing 1's and 0's, as Roy originally did, ensures that >he's not having a read-mofdify-write problem... Which he WOULD have >had if he used your code with his original hardware (i.e., without a >pullup on RA4). Actually, his code compiles to bcf and bsf instructions, too, which are RMW instructions. Perhaps that's the original source of his problems? Anything of the sort Rn = 0; or Rn = 1; compiles to a bcf or bsf instructions in HI-TECH., regardless of optimization level. -- ______________________________________ Andrew E. Kalman, Ph.D. RemoveMEaekEraseMEEraseMEpumpkininc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservspam_OUTKILLspammitvma.mit.edu with SET PICList DIGEST in the body

----- Original Message ----- From: "Andrew E. Kalman" <RemoveMEaekTakeThisOuTspamPUMPKININC.COM> To: <EraseMEPICLISTspamspamBeGoneMITVMA.MIT.EDU> Sent: Friday, June 29, 2001 6:12 PM Subject: Re: [PIC]: 16c73 RA4 as I/O will not work {Quote hidden}> Andy Warren wrote: > > >Explicitly writing 1's and 0's, as Roy originally did, ensures that > >he's not having a read-mofdify-write problem... Which he WOULD have > >had if he used your code with his original hardware (i.e., without a > >pullup on RA4). > > Actually, his code compiles to bcf and bsf instructions, too, which > are RMW instructions. Perhaps that's the original source of his > problems? Yes, but the bit being set or cleared is the one in question, so it can't cause the typical RMW problem. The RMW problem with BCF/BSF happens on _other_ bits within the same port. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Bob Ammerman wrote: > > Actually, his code compiles to bcf and bsf instructions, too, which >> are RMW instructions. Perhaps that's the original source of his >> problems? > >Yes, but the bit being set or cleared is the one in question, so it can't >cause the typical RMW problem. The RMW problem with BCF/BSF happens on >_other_ bits within the same port. Good -- now that's cleared up in my mind. To bad the PIC doesn't have a btf (bit toggle flag) instruction -- in that case PORTA ^= 0x40 would be the perfect solution. -- ______________________________________ Andrew E. Kalman, Ph.D. aekSTOPspamspam_OUTpumpkininc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservSTOPspamEraseMEmitvma.mit.edu with SET PICList DIGEST in the body

> To bad the PIC doesn't have a btf (bit toggle flag) instruction -- in > that case PORTA ^= 0x40 would be the perfect solution. The 18C _does_ have such an instruction Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body

Bob Ammerman <EraseMEPICLISTEraseMEmitvma.mit.edu> wrote: > > To bad the PIC doesn't have a btf (bit toggle flag) instruction -- > > in that case PORTA ^= 0x40 would be the perfect solution. > > The 18C _does_ have such an instruction As do the PIC17 parts. -Andy === Andrew Warren --- @spam@aiw@spam@spam_OUTcypress.com === IPD Systems Engineering, CYSD === Cypress Semiconductor Corporation === === Opinions expressed above do not === necessarily represent those of === Cypress Semiconductor Corporation -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body