Post by thread:Implementing RS-232 serial with 16F876 UART

I am using a 16F876 for a project and need to implement standard asynchronous RS-232 serial transmission (and reception) for part of it. Unfortunately, after exploring the PICLIST archives and the small amount of documentation Microchip has on the subject, I have been unable to successfully send or receive data over a serial port to terminal software. I have found some samples from the PICLIST search that seemed like they would work, but again I have been unsuccessful. Time is becoming an issue, and I would greatly appreciate any help I could get. Because so many things are involved with serial communication, it is hard to track down what is going wrong. And, unfortunately, no code I have seen is complete from the start to beginning. Can someone possibly give me an entire source file that they have confirmed works, that simply transmits and receives a few characters? Also, everything I have read only seems to mention using the Tx and Rx pins on Port C. Are connecting these pins to the opposite pins on a serial port all that is needed? Is there no need for any RTS/CTS connections etc? Thanks for your time and any help you can give. Below are the details of my configuration. Please be patient as I have limited experience. Using PIC 16F876 4.000 MHz OSC Powered at 5V TTL Programming in Microchip MPLAB 4.99.07 with Picstart PLUS programmer 2.01.00 Thanks again! -Josh http://www.jwardell.com

On Sat, 1 Apr 2000, Josh Wardell wrote: {Quote hidden}> I am using a 16F876 for a project and need to implement standard > asynchronous RS-232 serial transmission (and reception) for part of it. > Unfortunately, after exploring the PICLIST archives and the small amount of > documentation Microchip has on the subject, I have been unable to > successfully send or receive data over a serial port to terminal software. I > have found some samples from the PICLIST search that seemed like they would > work, but again I have been unsuccessful. Time is becoming an issue, and I > would greatly appreciate any help I could get. > Because so many things are involved with serial communication, it is hard > to track down what is going wrong. And, unfortunately, no code I have seen > is complete from the start to beginning. Can someone possibly give me an > entire source file that they have confirmed works, that simply transmits and > receives a few characters? > Also, everything I have read only seems to mention using the Tx and Rx > pins on Port C. Are connecting these pins to the opposite pins on a serial > port all that is needed? Is there no need for any RTS/CTS connections etc? > Thanks for your time and any help you can give. Below are the details of > my configuration. Please be patient as I have limited experience. > > Using PIC 16F876 > 4.000 MHz OSC > Powered at 5V TTL > Programming in Microchip MPLAB 4.99.07 > with Picstart PLUS programmer 2.01.00 Josh, I haven't used a 'real' 16F876, however I've studied it quite a bit in developing a simulatable version for gpsim. While searching the archives you may've ran across my post on this subject. In the past week or so, I've updated the sample code that illustrates how the uart can be programmed. This is a simple example that I use only for testing gpsim. There are probably much better examples that target other processors than the 16f876. But keep in mind that they all implement the same uart (AFAIK). So you may be better off trying to search for uart drivers for the C65 or C74. But here's the example http://cvs.sourceforge.net/cgi-bin/cvsweb.cgi/~checkout~/examples/14bit/usart_14.asm?rev=1.2&content-type=text/plain&cvsroot=gpsim (which may wrap around in your mail reader) In general, you can view this and other examples in gpsim's CVS repository at: http://cvs.sourceforge.net/cgi-bin/cvsweb.cgi/examples/?cvsroot=gpsim Scott

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 > Also, everything I have read only seems to mention using the Tx and Rx >pins on Port C. Are connecting these pins to the opposite pins on a serial >port all that is needed? Is there no need for any RTS/CTS connections etc? > Thanks for your time and any help you can give. Below are the details of >my configuration. Please be patient as I have limited experience. Serial is great fun.. Your terminal program may ignore input without handshakes present. Most don't care. The terminal program with Win95/8 dosen't care. I bought a cheap surplus data line monitor for $20, it's served me well. A $5 wyse-50 terminal is another good choice, as it can be put into a mode that will show you the hex values of whatever it sees. On RX and TX.. Make some noise on one of them, connecting it to ground will do. If you get junk on the screen, (garbage chars) then this is the lead you need to talk into. The other one is what you listen to. Some devices are labelled in the conventional way, TX meaning "data coming out" and others are labelled TX meaning "I want the other device's data out lead connected here". You have to produce a start bit, 8 data bits, and then return the line back to idle for at least one bit time (stop bit) Probably the easiest chars to get started with are $AA and $55 since the bit-patterns are 10101010 and 01010101 That way, it's easy to scope the bits. You should already know this, but your bit timing has to be accurate, 2.5% error is as much as I'd reccomend, since the last bit can't be off more than half a bit-time. (2.5% would be off 1/4 bit-time) Another thing to watch, you need to make sure you've finished sending the first byte (including stop bit) before sending the next byte. That's an easy one to get wrong :) Start out at low speeds, since it's easier to get the timing right (especially bit-banging!) Good luck! -----BEGIN PGP SIGNATURE----- Version: PGPfreeware 6.5.2 for non-commercial use <http://www.pgp.com> iQA+AwUBOOaS8oFlGDz1l6VWEQIWgQCg5uAd4NNuCCorTle2X8130OVxNrQAkQFA /5T42hy6p23zvngQKV4+2fQ= =bIxd -----END PGP SIGNATURE-----

<x-flowed>An excellent book which covers serial communications on a pic is Serial PIC'n by Roger L. Stevens. There are tons of code samples, including using on-chip UARTs, bit banging, I2C, SPI, and other interfaces/protocols. A great 'start bit' for learning PIC serial comm. :) - Mike At 03:45 PM 4/1/2000 -0500, you wrote: {Quote hidden}> I am using a 16F876 for a project and need to implement standard >asynchronous RS-232 serial transmission (and reception) for part of it. >Unfortunately, after exploring the PICLIST archives and the small amount of >documentation Microchip has on the subject, I have been unable to >successfully send or receive data over a serial port to terminal software. I >have found some samples from the PICLIST search that seemed like they would >work, but again I have been unsuccessful. Time is becoming an issue, and I >would greatly appreciate any help I could get. > Because so many things are involved with serial communication, it is hard >to track down what is going wrong. And, unfortunately, no code I have seen >is complete from the start to beginning. Can someone possibly give me an >entire source file that they have confirmed works, that simply transmits and >receives a few characters? > Also, everything I have read only seems to mention using the Tx and Rx >pins on Port C. Are connecting these pins to the opposite pins on a serial >port all that is needed? Is there no need for any RTS/CTS connections etc? > Thanks for your time and any help you can give. Below are the details of >my configuration. Please be patient as I have limited experience. > >Using PIC 16F876 >4.000 MHz OSC >Powered at 5V TTL >Programming in Microchip MPLAB 4.99.07 >with Picstart PLUS programmer 2.01.00 > > Thanks again! > > -Josh > http://www.jwardell.com </x-flowed>

> > On Sat, 1 Apr 2000, Josh Wardell wrote: > >> I am using a 16F876 for a project and need to implement standard >> asynchronous RS-232 serial transmission (and reception) for part of it. >> Unfortunately, after exploring the PICLIST archives and the small amount of >> documentation Microchip has on the subject, I have been unable to >> successfully send or receive data over a serial port to terminal software. Another working prototype with code is in Tony Nixon's ROMZap. ROMZap uses the serial port to download code into 16F87X parts. It initializes the port. So you can use it as a working example. http://www.picnpoke.com BAJ

Hi, Just a thought, ( don't know how much You know about comms. ) >Also, everything I have read only seems to mention using the Tx and Rx >pins on Port C. Are connecting these pins to the opposite pins on a serial >port all that is needed? Is there no need for any RTS/CTS connections etc? >Thanks for your time and any help you can give. Below are the details of >my configuration. Please be patient as I have limited experience. This sounds like You are trying to connect the RS232 pins from the computer directly to the PIC, is this the case ? then no go, You must use an level shifter of some sorts to accomplish the 'correct' ( not that sensitive ) voltage levels. For exemple any MAX232... I can supply you with some options if this is the case. Secondly to answer Your question, you need to connect: Pic:Rx -> Pc:Tx ( level shifter ! ) Pic:Tx -> Pc:Rx ( level shifter ! ) Pic:Gnd -> Pc:Gnd ( straight connection ) Assuming that no handshaking is used. /Tony Tony KŸbek, Flintab AB ÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓ E-mail: spam_OUTtony.kubekTakeThisOuTflintab.com ÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓ

Some designs for RS232 interfacing: ; Simple RS232C - PC to PIC Interface Aug/94 T. Rudersdorfer, AScT ; revised Sep/94 ; ; 1 - 470 ohm short circuit current limit ; 1 - 10k open collecter pull down ; 1 - 47k power up pull up ; 1 - 470k injection current limit ; 2 - 15pf oscillator stabilization ; 1 - .1uf decouple PIC and regulator ; 1 - 10uf voltage stabilization ; 1 - 5.0688MHz standard communication xtal ; 1 - 1N4150 reverse voltage blocking diode ; 1 - 78L05 5V low power regulator (100mA Max) ; 1 - 16C84 PIC ; 1 - LED do something test led ; 1 - 2k7 do something current limit for test led ; ; PC DTE DCE ; ; RX<(3)--(3)-/\/\/\/-----------------------------+--/\/\/\/----+ ; 470 | 10k | ; |\ | | /// ; +-----/\/\/\/--| >|---------------------+ | ; | 2k7 |/ | --------------- | | ; | LED | 1 U RA1 |--+ | ; | ^ +5V | RA0 |----+ ; | | | ____ 1 Osc1 |------------------+ ; +---+-/\/\/\/--------| MCLR 6 Osc2 |------+ | ; 47k +-----| Vss C Vdd |--+ | _ | ; | +--| RB0 8 | | +---||_||---+ ; /// | | 4 | | | 5.0688MHz | ; TX>(2)--(2)-/\/\/\/-----+ | | | _|_ _|_ ; 470k |_______________| | ___15pf ___15pf ; | | | ; 1N4150 _____ ^ +5V | /// /// ; |\ | | | | | ; RTS>(4)--(4)-+----| >|----+---|78L05|---+------+ ; | |/ | | 1|_____|3 | ; CTS<(5)--(5)-+ _|_ |2 _|_ ; | ___10uf | ___.1uf ; DSR<(6)--(6)-+ | | | ; /// /// /// ; GND (7)--(7)-+ ; | ; /// ; ; RS232 RX circuit background: ; Based on AN521 in the 1993 Embedded Handbook; PIC I/O pins can handle ; +/- 500uA of continuous injected current. This means voltages greater ; than VDD and VSS CAN BE used as long as adequate current limiting is ; provided. My original RX input design isolated the PIC by using an ; extra transistor, diode and resistor. This can be eliminated by using ; a large enough resistor value in series to the PIC I/O Pin. RS232 ; voltage levels can be up to +/- 15V, therefore, a 470k resistor provides ; an adequate current limit of 32uA (the same current used in AN521). ; ; RS232 TX circuit background: ; Researching specification sheets for RS232 receivers like the 1489, ; reveals that they do not require bipolar voltages to operate. The ; 1489 in fact clips all -ve signals to ground, therefore only requiring ; +ve and ground input levels. Or have a look at the image at http://www.ise.pw.edu.pl/~wzab/picadc/picadc.html ( on the middle of the page ) /Tony Tony KŸbek, Flintab AB ÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓ E-mail: .....tony.kubekKILLspam@spam@flintab.com ÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓ

I'd suggest a small improvement, to limit the input voltage from the PC's TX line: TX<(2)--(2)-/\/\/\/-------------+-----/\/\/\/---+--/\/\/\/----+ 10k | X 10k | 40k | | /| | | /| | /// +5V <--|< |---+--|< |---+ +---- RB0 | \| | \| | /// When TX goes high, the voltage in node X is equal to 5.7V so the voltage on RB0 is equal to 5.7V*4/5=4.56V. No danger for PIC at all !!! Similarly the diode/voltage divider can limit the reverse input current (however it is a little more difficult to explain - consider the Shockley's equation ;-) ). HTH Wojciech Zabolotny wzabKILLspamise.pw.edu.pl On Mon, 3 Apr 2000, [Iso-8859-1] Kübek Tony wrote: {Quote hidden}> Some designs for RS232 interfacing: > > ; Simple RS232C - PC to PIC Interface Aug/94 T. Rudersdorfer, > AScT > ; revised Sep/94 > ; > ; 1 - 470 ohm short circuit current limit > ; 1 - 10k open collecter pull down > ; 1 - 47k power up pull up > ; 1 - 470k injection current limit > ; 2 - 15pf oscillator stabilization > ; 1 - .1uf decouple PIC and regulator > ; 1 - 10uf voltage stabilization > ; 1 - 5.0688MHz standard communication xtal > ; 1 - 1N4150 reverse voltage blocking diode > ; 1 - 78L05 5V low power regulator (100mA Max) > ; 1 - 16C84 PIC > ; 1 - LED do something test led > ; 1 - 2k7 do something current limit for test led > ; > ; PC DTE DCE > ; > ; RX<(3)--(3)-/\/\/\/-----------------------------+--/\/\/\/----+ > ; 470 | 10k | > ; |\ | | /// > ; +-----/\/\/\/--| >|---------------------+ | > ; | 2k7 |/ | --------------- | | > ; | LED | 1 U RA1 |--+ | > ; | ^ +5V | RA0 |----+ > ; | | | ____ 1 Osc1 |------------------+ > ; +---+-/\/\/\/--------| MCLR 6 Osc2 |------+ | > ; 47k +-----| Vss C Vdd |--+ | _ | > ; | +--| RB0 8 | | +---||_||---+ > ; /// | | 4 | | | 5.0688MHz | > ; TX>(2)--(2)-/\/\/\/-----+ | | | _|_ _|_ > ; 470k |_______________| | ___15pf ___15pf > ; | | | > ; 1N4150 _____ ^ +5V | /// /// > ; |\ | | | | | > ; RTS>(4)--(4)-+----| >|----+---|78L05|---+------+ > ; | |/ | | 1|_____|3 | > ; CTS<(5)--(5)-+ _|_ |2 _|_ > ; | ___10uf | ___.1uf > ; DSR<(6)--(6)-+ | | | > ; /// /// /// > ; GND (7)--(7)-+ > ; | > ; /// > ; > ; RS232 RX circuit background: > ; Based on AN521 in the 1993 Embedded Handbook; PIC I/O pins can > handle > ; +/- 500uA of continuous injected current. This means voltages > greater > ; than VDD and VSS CAN BE used as long as adequate current limiting > is > ; provided. My original RX input design isolated the PIC by using an > ; extra transistor, diode and resistor. This can be eliminated by > using > ; a large enough resistor value in series to the PIC I/O Pin. RS232 > ; voltage levels can be up to +/- 15V, therefore, a 470k resistor > provides > ; an adequate current limit of 32uA (the same current used in AN521). > ; > ; RS232 TX circuit background: > ; Researching specification sheets for RS232 receivers like the 1489, > ; reveals that they do not require bipolar voltages to operate. The > ; 1489 in fact clips all -ve signals to ground, therefore only > requiring > ; +ve and ground input levels. > > Or have a look at the image at > http://www.ise.pw.edu.pl/~wzab/picadc/picadc.html > ( on the middle of the page ) >

Anyone know what e bookstores stock serial pic'n'? Amazon and Bol draw blanks. Uk sources would be best but not essential. Also Can anyone tell me what the advantage and disadvantages of wiring CTS and RTS in a pic to pc application. I have to wire the hardware now for so don't want to find i should have wired the PCB another way. Regards Scott >22222222222222222222222222222222222222222222222222222222 -- ******************************************* Broadcast Warehouse, Fm transmitters Po box 697, wallington, surrey, SM67ZR U.K. tel: +44 (0) 20 8288 0192 fax: +44 (0) 20 8288 0609 web: http://www.broadcast-warehouse.com email: .....infoKILLspam.....broadcast-warehouse.com *******************************************

part 0 3053 bytes Scott, Try: <A HREF="http://www.amazon.com/exec/obidos/ASIN/0965416224/qid%3D954798740/103-4149132-8117410" TARGET="_blank">www.amazon.com/exec/obidos/ASIN/0965416224/qid%3D954798740/103-4149132-8117410</A> It's AMAZON.COM and I was able to locate it. Best regards, Steve Steven Kosmerchock Father/Student/Engineering Technician http://www.geocities.com/researchtriangle/lab/6584 "Great spirits have always encountered violent oppposition from mediocre minds."--A.Einstein {Original Message removed}

Josh, I went to your web site as listed below, and wow, do you have nice graphics on those first two introductory pages. Is this a hand-held o'scope based on a palm V? Sean At 09:07 PM 4/3/00 -0400, you wrote: {Quote hidden}> I wanted to thank all of you for all your help in getting my PIC to speak >232, and apologize for not personally responding to each of your emails. My >biggest problem was that I was not aware of the need for a 232 driver chip. >After getting a hold of one off of another board today and a bit of reverse >engineering, I'm happy to say my pic is successfully talking to my palm >pilot. Thanks again for all your help! > > -Josh > http://www.jwardell.com/about/seniorproj/index.html > | | Sean Breheny | Amateur Radio Callsign: KA3YXM | Electrical Engineering Student \--------------=---------------- Save lives, please look at http://www.all.org Personal page: http://www.people.cornell.edu/pages/shb7 @spam@shb7KILLspamcornell.edu ICQ #: 3329174

> ; RX<(3)--(3)-/\/\/\/-----------------------------+--/\/\/\/----+ > ; 470 | 10k | > ; |\ | | /// > ; +-----/\/\/\/--| >|---------------------+ | > ; | 2k7 |/ | --------------- | | > ; | LED | 1 U RA1 |--+ | > ; | ^ +5V | RA0 |----+ That sender is a very bad one. You will send a LOW with only 0V and 10k5 output resistance. An RS232C LOW must be -3V or lower, and be sent with lower resistance. Your 10k5 are in the magnitude of pullup resistors, not drivers. Imagine someone places 10k pullup on the host side, that will build a resistor divider that leaves RX at 6V for LOW (!) (when the host is using 12V reference voltage).

On Tue, Apr 04, 2000 at 12:29:53PM +0000, Marc wrote: > > ; RX<(3)--(3)-/\/\/\/-----------------------------+--/\/\/\/----+ > > ; 470 | 10k | > > ; |\ | | /// > > ; +-----/\/\/\/--| >|---------------------+ | > > ; | 2k7 |/ | --------------- | | > > ; | LED | 1 U RA1 |--+ | > > ; | ^ +5V | RA0 |----+ > > That sender is a very bad one. You will send a LOW with only 0V and 10k5 > output resistance. An RS232C LOW must be -3V or lower, and be sent with > lower resistance. Your 10k5 are in the magnitude of pullup resistors, > not drivers. Imagine someone places 10k pullup on the host side, that > will build a resistor divider that leaves RX at 6V for LOW (!) (when the > host is using 12V reference voltage). Most RS232 ports in PC work fine with 0V<->5V voltage levels (yes, I know it contradicts the RS232 standard and decreases the noise margin =:-( but this is the sad true.) Why do you think, that in LOW state the output resistance is 10k5? In fact if the RA0 was open drain, the HIGH resistance would be 10k5, but AFAIK the RA0 is normal CMOS output. -- Greetings Wojciech M. Zabolotny http://www.ise.pw.edu.pl/~wzab <--> KILLspamwzabKILLspamise.pw.edu.pl http://www.ise.pw.edu.pl/~wzab/picadc/picadc.html - Build your FREE Data Acquisition System