Post by thread:RS232 levels -> TTL

I'm wondering if there is an easy way to convert RS232 output to levels suitable for a PIC. Like perhaps stripping the negative voltage with a diode and running the remainder through a transistor or something? Any pointers would be helpful. Regards, Mattias Engstrom -- ------------------------------------------- BassLab Production, Mix, Remix fascility Mail us : spam_OUTbasslabTakeThisOuTusa.net Call us : +46-(0)708-833331 -------------------------------------------

On Mon, 13 Oct 1997, Mattias Engstrvm wrote: > I'm wondering if there is an easy way to convert RS232 output to levels > suitable for > a PIC. Like perhaps stripping the negative voltage with a diode and > running the remainder through a transistor or something? > Take a look at http://www.maxim-ic.com. Maxim makes a wide range of RS232 line driver/receivers. I frequently use the MAX233 - single +5v supply and no external components. Dave Gilinsky (DG75) Pixel Dust, Inc. .....daveKILLspam@spam@gaspra.once-ler.com _______________________________________________________________________________

On Mon, 13 Oct 1997, Dave Gilinsky wrote: > On Mon, 13 Oct 1997, Mattias Engstrvm wrote: > > > I'm wondering if there is an easy way to convert RS232 output to levels > > suitable for > > a PIC. Like perhaps stripping the negative voltage with a diode and > > running the remainder through a transistor or something? > > > > Take a look at http://www.maxim-ic.com. Maxim makes a wide range of RS232 line > driver/receivers. I frequently use the MAX233 - single +5v supply and no > external components. The MAX232 or Dallas 232A are fine. They have 2 send and 2 receive and need about 4 charge capas, 1.0uF, and a decoupling cap. There are others that have more send and/or receive channels. Rob > > > Dave Gilinsky (DG75) > Pixel Dust, Inc. > daveKILLspamgaspra.once-ler.com > _______________________________________________________________________________ >

Mattias: I have used this network for years and it seems to work with all versions of the RS232 drives. o + 5V | > < 10 K > RS232 20 K | o-----/\/\/\/--+-|<|---+----o Pic | 1N4148 or dual SMT diode --|<|---| Gnd ---- -- - Wayne Foletta {Quote hidden}> ---------- > From: Mattias Engstrvm[SMTP:.....maten149KILLspam.....STUDENT.LIU.SE] > Sent: Monday, October 13, 1997 9:34 AM > To: EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU > Subject: RS232 levels -> TTL > > I'm wondering if there is an easy way to convert RS232 output to > levels > suitable for > a PIC. Like perhaps stripping the negative voltage with a diode and > running the remainder through a transistor or something? > > Any pointers would be helpful. > > Regards, Mattias Engstrom > > -- > ------------------------------------------- > BassLab > Production, Mix, Remix fascility > Mail us : basslabspam_OUTusa.net > Call us : +46-(0)708-833331 > ------------------------------------------- >

At 9:34 AM -0700 10/13/97, Mattias Engstrvm wrote: >I'm wondering if there is an easy way to convert RS232 output to levels >suitable for >a PIC. Like perhaps stripping the negative voltage with a diode and >running the remainder through a transistor or something? > >Any pointers would be helpful. > >Regards, Mattias Engstrom > >-- >------------------------------------------- > BassLab > Production, Mix, Remix fascility > Mail us : @spam@basslabKILLspamusa.net > Call us : +46-(0)708-833331 >------------------------------------------- Place a 100K resistor in-line with the RS-232 signal of interest. The internal clamping diodes will shunt the excess + voltage to VCC and the excess - voltage to VSS (ground). Make sure you connect the RS-232 GROUND to your VSS. Otherwise, you can get random results if you get anything at all. (Classic example is it working great when looking at it with a scope probe!) If you want to be extra careful, you can place a 100K series resistor on the RS-232 ground connection. cheers, eric

Use an RS232 level converter, try the Maxim MAX232, or one of its many derivatives. ______________________________ Reply Separator _________________________________ Subject: RS232 levels -> TTL Author: KILLspamPICLISTKILLspamMITVMA.MIT.EDU (Mattias Engstrvm) at uk-internet Date: 10/13/97 5:34 PM I'm wondering if there is an easy way to convert RS232 output to levels suitable for a PIC. Like perhaps stripping the negative voltage with a diode and running the remainder through a transistor or something? Any pointers would be helpful. Regards, Mattias Engstrom -- ------------------------------------------- BassLab Production, Mix, Remix fascility Mail us : RemoveMEbasslabTakeThisOuTusa.net Call us : +46-(0)708-833331 -------------------------------------------

I've seen and used (on the bench - with 16x84) a circuit that puts a 33k-ohm resistor in series with the RS232 input to the PIC. I guess this brings the reverse current into the range handled by the internal protection diodes. Although the forward voltage is high - again, It wold appear that the input protection can deal with +12V/33k .... The result. It works well enough at 9600bps - I haven't tried any higher, but I haven't seen any missed bits yet. I would probably put a level translator into production items though, as the resistor just doesn't seem 'right' ! P.S. Remember that RS232 line levels are NEGATIVE logic... -12V = MARK +12V = SPACE. Regards MC -----Original Message----- From: Mattias Engstrvm [SMTP:spamBeGonematen149spamBeGoneSTUDENT.LIU.SE] Sent: Tuesday, October 14, 1997 12:34 AM To: TakeThisOuTPICLISTEraseMEspam_OUTMITVMA.MIT.EDU Subject: RS232 levels -> TTL I'm wondering if there is an easy way to convert RS232 output to levels suitable for a PIC. Like perhaps stripping the negative voltage with a diode and running the remainder through a transistor or something? Any pointers would be helpful. Regards, Mattias Engstrom

Bob Lunn 10/14/97 11:49 AM >> Take a look at http://www.maxim-ic.com. Maxim makes a wide range of RS232 line >> driver/receivers. I frequently use the MAX233 - single +5v supply and no >> external components. > > The MAX232 or Dallas 232A are fine. They have 2 send and 2 receive and > need about 4 charge capas, 1.0uF, and a decoupling cap. Personally, I like the MAX201 -- which requires only a couple of external 0.1uf caps. It's a good compromise between the '233 (no external components, but expensive) and the '232 (cheap, but four bulky external caps). ___Bob

Mattias Engstrvm wrote: > > I'm wondering if there is an easy way to convert RS232 output to levels > suitable for > a PIC. Like perhaps stripping the negative voltage with a diode and > running the remainder through a transistor or something? > > Any pointers would be helpful. Ok, I'm going to put my foot in it... This thread invoked some creative circuitry some time ago. The absolute easiest way that has *never, ever* failed me on any PC-based notebook, desktop or anything with a RS232 driver in it, is a simple transistor inverter. Get 12V from the RS232 port on your PC, feed it through a 10k resistor to the collector of *any* NPN transistor. Ground the emittor. The input is via a 10k resistor onto the base, and the output is on the collector. Easy. Simple. Effective. -- Friendly Regards Tjaart van der Walt RemoveMEtjaartTakeThisOuTwasp.co.za _____________________________________________________________ | WASP International http://www.wasp.co.za/~tjaart/index.html | | R&D Engineer : GSM peripheral services development | | Vehicle tracking | Telemetry systems | GSM data transfer | | Voice : +27-(0)11-622-8686 | Fax : +27-(0)11-622-8973 | | WGS-84 : 26010.52'S 28006.19'E | |_____________________________________________________________|

> Mattias Engstrvm wrote: > > > > I'm wondering if there is an easy way to convert RS232 output to levels > > suitable for > > a PIC. Like perhaps stripping the negative voltage with a diode and > > running the remainder through a transistor or something? I've used this circuit a lot - it works every time. It originally came from an Intel 8051 data book. Note that as shown, the RxD is inverted (i.e. mark is logic low). If required, use an inverter on it before the input to the chip. You could use a transistor for this, or any 74x04 type inverter. You might also want another clamp diode from RxD to +5. +5V | | / 10K or so ||/ PNP TxD --/\/\/\/--------| - |\ | \ | +-------------------- RS232 out -> | | \ 1K or so / \ / Gnd +| | | --------| |----+ 10uF | | | \|/ ----- | RxD --+---/\/\/\/\-----+-------------------- RS232 in <- | 10K mebbe \|/ ------ | | Gnd -- Clyde Smith-Stubbs | HI-TECH Software Email: clydeEraseME.....htsoft.com | Phone Fax WWW: http://www.htsoft.com/ | USA: (408) 490 2885 (408) 490 2885 PGP: finger EraseMEclydehtsoft.com | AUS: +61 7 3354 2411 +61 7 3354 2422 --------------------------------------------------------------------------- ANSI C for the PIC! Now shipping! See http://www.htsoft.com for more info.

In message <RemoveMEPine.BSI.3.95.971013123730.20073A-100000EraseMEEraseMEns.hicom.net>> RemoveMEPICLISTspam_OUTKILLspamMITVMA.MIT.EDU writes: > On Mon, 13 Oct 1997, Dave Gilinsky wrote: > > > On Mon, 13 Oct 1997, Mattias Engstrvm wrote: > > > > > I'm wondering if there is an easy way to convert RS232 output to levels > > > suitable for > > > a PIC. Like perhaps stripping the negative voltage with a diode and > > > running the remainder through a transistor or something? > > > > > > > Take a look at http://www.maxim-ic.com. Maxim makes a wide range of RS232 line > > driver/receivers. I frequently use the MAX233 - single +5v supply and no > > external components. > > The MAX232 or Dallas 232A are fine. They have 2 send and 2 receive and > need about 4 charge capas, 1.0uF, and a decoupling cap. There are others > that have more send and/or receive channels. > Another one to look out for is the MAX3232. This has an extended vcc range: 2.5V to 5.5V IIRC in tests I had it and a C71 sending data to a PC at under 2V. Regards, Mike Watson

Mattias: I have used this network for years and it seems to work with all versions of the RS232 port drives. o + 5V | > < 10 K > RS232 20 K | o-----/\/\/\/--+-|<|---+----o Pic | 1N4148 or dual SMT diode --|<|---| Gnd ---- -- - Wayne Foletta {Quote hidden}> ---------- > From: Mattias Engstrvm[SMTP:RemoveMEmaten149TakeThisOuTspamSTUDENT.LIU.SE] > Sent: Monday, October 13, 1997 9:34 AM > To: EraseMEPICLISTspamspamBeGoneMITVMA.MIT.EDU > Subject: RS232 levels -> TTL > > I'm wondering if there is an easy way to convert RS232 output to > levels > suitable for > a PIC. Like perhaps stripping the negative voltage with a diode and > running the remainder through a transistor or something? > > Any pointers would be helpful. > > Regards, Mattias Engstrom > > -- > ------------------------------------------- > BassLab > Production, Mix, Remix fascility > Mail us : RemoveMEbasslabKILLspamusa.net > Call us : +46-(0)708-833331 > ------------------------------------------- > >

Mattias: I have used this network for years and it seems to work with all versions of the RS232 port drives. o + 5V | > < 10 K > RS232 20 K | o-----/\/\/\/--+-|<|---+----o Pic | 1N4148 or dual SMT diode --|<|---| Gnd ---- -- - Wayne Foletta {Quote hidden}> ---------- > From: Mattias Engstrvm[SMTP:maten149STOPspamspam_OUTSTUDENT.LIU.SE] > Sent: Monday, October 13, 1997 9:34 AM > To: spamBeGonePICLISTSTOPspamEraseMEMITVMA.MIT.EDU > Subject: RS232 levels -> TTL > > I'm wondering if there is an easy way to convert RS232 output to > levels > suitable for > a PIC. Like perhaps stripping the negative voltage with a diode and > running the remainder through a transistor or something? > > Any pointers would be helpful. > > Regards, Mattias Engstrom > > -- > ------------------------------------------- > BassLab > Production, Mix, Remix fascility > Mail us : KILLspambasslabspamBeGoneusa.net > Call us : +46-(0)708-833331 > ------------------------------------------- > > > >

Dear Mattias This will work fine with the PIC's. Keep in mind that on the mid-range input pin RA4 looks different. It is configured as open-drain output and it has protection diodes to VSS only. Regards, Christof On 13 Oct 97 at 12:40, Wayne Foletta wrote: {Quote hidden}> Mattias: > I have used this network for years and it seems to work with all > versions of the RS232 drives. > o + 5V > | > > > < 10 K > > > RS232 20 K | > o-----/\/\/\/--+-|<|---+----o Pic > | 1N4148 or dual SMT diode > --|<|---| Gnd > ---- > -- > - Wayne Foletta > > > ---------- > > From: Mattias Engstrvm[SMTP:EraseMEmaten149EraseMESTUDENT.LIU.SE] > > Sent: Monday, October 13, 1997 9:34 AM > > To: @spam@PICLIST@spam@spam_OUTMITVMA.MIT.EDU > > Subject: RS232 levels -> TTL > > > > I'm wondering if there is an easy way to convert RS232 output to > > levels > > suitable for > > a PIC. Like perhaps stripping the negative voltage with a diode and > > running the remainder through a transistor or something? > > > > Any pointers would be helpful. > > > > Regards, Mattias Engstrom > > > > -- > > ------------------------------------------- > > BassLab > > Production, Mix, Remix fascility > > Mail us : spamBeGonebasslabKILLspamusa.net > > Call us : +46-(0)708-833331 > > ------------------------------------------- > > > >

{Quote hidden}> >Dear Mattias > >This will work fine with the PIC's. Keep in mind that on the mid-range input >pin RA4 looks different. It is configured as open-drain output and it has >protection diodes to VSS only. > >Regards, >Christof > > On 13 Oct 97 at 12:40, Wayne Foletta wrote: > >> Mattias: >> I have used this network for years and it seems to work with all >> versions of the RS232 drives. >> o + 5V >> | >> > >> < 10 K >> > >> RS232 20 K | >> o-----/\/\/\/--+-|<|---+----o Pic >> | 1N4148 or dual SMT diode >> --|<|---| Gnd >> ---- >> -- >> - Wayne Foletta >> Actually, the above should work with almost any CMOS input, although would I swap the values of the pullup and input resistors. It does not rely upon the internal pin protection diodes of the part at all. Observe: if the input is positive (greater than +5V), both diodes are reverse biased. The port pin is pulled up to VDD by the 10K pullup resistor. When the input is negative (less than -10V with the resistors shown above or less than -3V with the input & pullup resistors swapped), the port pin is at 0 Vdc. As the input goes negative, the lower diode begins to conduct and clamps the common point of the 2 diodes to about -0.7Vdc. The forward drop of the upper diode brings the PIC pin to about 0Vdc. The region between -3V and about +3V is undefined, just as it is in the RS-232 spec. Dwayne Reid <.....dwaynerspam_OUTplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, Alberta, CANADA (403) 489-3199 voice (403) 487-6397 fax