RS-232 specs are just about totally obsolete, but at the time they meant anything, they required that RS-232 receivers work with as little as +/- 3V and that they accept +/- 18V at least before failing. Signals between +3V and -3V are unspecified and therefore may generate an undetermined state. However, most recent (<10 years old) computers will work with unipolar TTL levels because the receivers have a bias point set slightly positive.
Didier KO4BB > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Hal Murray > Sent: Wednesday, February 13, 2008 12:05 AM > To: Darrell Robinson > Cc: [email protected] > Subject: Re: [time-nuts] Trimble Thunderbolt Rs-232 Levels > > > > I think I will apply power to the module and measure the > levels from > > the port. If it is TTL out, I will need to do a level > shift anyway to > > give the computer proper voltages to run it's serial port. > > Most RS-232 level shifters also include an inverter. > > I'd just plug it in and see if it works. Especially if it has a DB-9. > > Ages ago, RS-232 specs called for 12 V. I think they updated > it to work at 6V. > > In practice TTL signals actually work, at least if you aren't > using long cables. All the receiver chips I've checked have > had an input threshold at roughly the TTL switching level - 2 > diode drops above ground. > > > > -- > These are my opinions, not necessarily my employer's. I hate spam. > > > > > _______________________________________________ > 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 incoming message. > Checked by AVG Free Edition. > Version: 7.5.516 / Virus Database: 269.20.4/1275 - Release > Date: 2/12/2008 3:20 PM > > No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.20.4/1277 - Release Date: 2/13/2008 8:00 PM _______________________________________________ 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.
