Hi Hooking the ~ +/- 10V output of a MAX 232 to one of it's CMOS logic inputs probably isn't a real good idea. Two resistors and a cheap transistor make a fine inverter in this case.
Bob On Jul 13, 2013, at 11:29 AM, ewkeh...@aol.com wrote: > Most MAX have two sets and one could use one as an inverter if one does not > want to add an extra IC. > Bert Kehren > > > In a message dated 7/13/2013 10:09:12 A.M. Eastern Daylight Time, > als...@nc.rr.com writes: > > Guys, > > The PIC in question was knowingly programmed "upside down" with the N > option so it could talk directly to the computer without an RS232 > converter. (input side suitably protected from -voltage levels) > > This works of most PC's which in actuality use 3.3 Volt logic in their > RS232 port and input clamp highs/lows to be within the logic family > limits. > > There are two serial port choices for a PIC in the PICAXE/BS2 compilers > N and T. > > From the PICAXE manual. > > "N idles low and T idles high. When using a simple resistor interface > use N (inverted) When using a MAX232 type interface use T" > > The bottom line is depending upon what your device is putting out and > what you are talking to you may or may not need an inverter for use with > the MAX232. > > Regards, > Brian > > On 7/13/2013 03:10, Chris Albertson wrote: >> You have it 100% correct. The UT+ uses "positive" logic are the logic 1 > is >> 5-volts but the RS-232 standard uses "negative" logic. I think the > MAX232 >> does the conversion correctly EXCEPT if you read the RS-232 standards > they >> use positive logic for the control signals. >> >> >> On Fri, Jul 12, 2013 at 7:34 PM, Bob Stewart <b...@evoria.net> wrote: >> >>> Hi Brian, >>> >>> That's just strange. There are a whole lot of these MAX232 and MAX3232 >>> devices being sold. Hmm, I'm looking at the UT+ User's Guide, and it > lists >>> the voltage levels as follows. These would imply that an inverter is >>> necessary, right? Could it be that someone programmed your PIC upside > down >>> - i.e. using negative logic? >>> >>> TTL >>> 0 V to 0.8 V = logic 0 >>> 2.4 V to 5.0 V = logic 1 >>> RS-232 (reordered from manual to put logic 0 on top) >>> 5 V to 15 V = logic 0 >>> -5 V to -15 V = logic 1 >>> >>> Bob - AE6RV >>> >>> >>> >>> >>>> ________________________________ >>>> From: Brian Alsop <als...@nc.rr.com> >>>> To: Bob Stewart <b...@evoria.net>; Discussion of precise time and >>> frequency measurement <time-nuts@febo.com> >>>> Sent: Friday, July 12, 2013 9:09 PM >>>> Subject: Re: [time-nuts] GPDSO is working >>>> >>>> >>>> Hi Bob, >>>> >>>> Here is my experience. I had a PIC that output RS232 at 0-5 volt >>>> levels. It actually worked with my computer directly. When I added a >>>> MAX 232 to make the levels something like -10/+10 volts. It didn't >>>> work. That's because the MAX232 inverts the polarity. Look at the > data >>>> sheet, the level converters are clearly inverters. >>>> >>>> The fix in my case was to invert the RS232 stream output by the PIC and >>>> all was fine. >>>> >>>> I'm not sure exactly what you have but a scope sorts it out quickly. >>>> >>>> 73 de Brian/K3KO >>>> >>>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> >> >> > > > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2012.0.2242 / Virus Database: 3204/5987 - Release Date: 07/12/13 > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.