Also, wikipedia has some recommendations but resisters at each cable end (resister has the same resistance as the cable's characteristic impedance.)
When it works at low speed but fails at higher speed this suggests some kind of cable setup issue. Perhaps wrong volts or wrong termination resisters On Thu, Dec 31, 2020 at 9:03 PM Chris Albertson <[email protected]> wrote: > I don't know much about RS485 but I did read that the current return path > is required. You should be able to send and about 100K up to 4000 feet. > > I'd use a section of Eithernet cable because I know it is twisted inside. > I don't know the best way to provide a "return path for all voltages" > > If this is going through optical isolators,I see a problem the signal > voltages are like RS232 −7V to +12V. The optos are going to do 0 to 5 > volts with is usually very marginal. > > On Thu, Dec 31, 2020 at 8:05 PM Gene Heskett <[email protected]> wrote: > >> On Thursday 31 December 2020 20:10:35 Chris Albertson wrote: >> >> > Now is the time to connect the digital scope and see what is actually >> > on the wire. Is the data bad or is the receiver unable to read good >> > quality 38400b data? >> > >> > This is differential data, it should be able to go half a kilometer or >> > something like that. Is it actuary using a twisted pair of wires and >> > is there a good logic ground? >> > >> That I doubt. Its a 2 wire cable, so any logic ground is coming thru >> other cable from the 5i25, thru the interfaceing and back to the ACM >> terminal. DCM could be grounded but is not, and everything on that >> circuit isvia the opto's isolating the spindle outputs of the 7i76D. >> >> That stuff is still hooked up, but could be disconnected as its no longer >> actually controlling the motor. There does not appear to be a ground >> reference for the rs485 signals called out in the sample wiring diagram. >> There is an earth ground in addition to the 2 wire single phase input, >> and its connected back to the static ground in the service box. >> >> > It's easy to see if the cable is the cause. look at the bits on the >> > cable end, then remove the cable and look at them in the output port. >> >> The only way I can access that would be to back the pins out of the term >> strip far enough to put the scope probe hook onto the Hilitchi pin. The >> scope is plugged into a different circuit entirely, so its ground >> reference is bound to have some noise on it. I can set the scope to >> combine the 2 signal wires into a differential, but having done that, >> the serialization of the samples quantizations can easily be seen. I >> should probably do that, if for no other reason than to confirm the baud >> rate matches going both ways. I have previously caught the pc lying >> about the actual baud rate its generating. Depending on the individual >> driver, it might be fixeable but haven't tried. From an lsmod: >> usbserial 31410 3 ftdi_sio >> and I've not had previous experience with the ftdi_sio being off. >> >> Since the lags can be gotten used to, I might just leave it at the slower >> speed as that seems to be bulletproof so far. >> >> Thanks Chris. And a Happier New Year to all. >> >> Cheers, Gene Heskett >> -- >> "There are four boxes to be used in defense of liberty: >> soap, ballot, jury, and ammo. Please use in that order." >> -Ed Howdershelt (Author) >> If we desire respect for the law, we must first make the law respectable. >> - Louis D. Brandeis >> Genes Web page <http://geneslinuxbox.net:6309/gene> >> >> >> _______________________________________________ >> Emc-users mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/emc-users >> > > > -- > > Chris Albertson > Redondo Beach, California > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
