On Sun, 05 Jan 2014 13:35:43 -0800 Hal Murray <[email protected]> wrote:
> > [email protected] said: > > Also keep in mind that RS-232 relies on the voltage going negative to encode > > a "1". I.e. getting 0V is not enough and might only work by chance with some > > RS-232 receivers. > > I think there are 2 parts to this discussion. What do the specs say, and > what actually happens in the real world? > > I think the specs say that -3 to +3 is no mans land. A valid signal must be > over +3 or under -3. IIRC that's right. But i haven't had a look at the standard for a very long time. > In practice, the receiver chip only has one power supply. It would take > extra work to make the switching threshold below ground. That's not correct. Standard transceiver chips (like the MAX232 family) have an integrated charge pump to get a negative power supply. I have never done exact measurements, but my experience is that going a bit (0.5V?) below GND and slightly more above GND is enough to get a proper 1/0 detection. Of course, if you rely on that you get a very poor noise performance. Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin _______________________________________________ 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.
