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, [email protected] 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 <[email protected]> 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 <[email protected]> >>> To: Bob Stewart <[email protected]>; Discussion of precise time and >> frequency measurement <[email protected]> >>> 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 -- [email protected] >> 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 -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
