On Tue, 2008-02-05 at 14:37 +1100, Erik Christiansen wrote: > On Sat, Feb 02, 2008 at 08:26:31PM -0800, Kirk Wallace wrote: > > http://pinouts.ru/SerialPortsCables/rs485_cable_pinout.shtml > > > > I plan on building a couple for my SJ200 application, and if you want I > > can make an extra and send it over. I'm not sure when I'll have time to > > build and test it -- probably in the next couple of weeks. Let me know. > > Hi Kirk, > > Though it looks like you're onto alternatives by now, it may be worth > noting that there's no separate network ground wire in that design. From > http://www.embeddedsys.com/subpages/resources/images/documents/microsys_art_RS485.pdf > , I'm planning to follow: > > "The RS-485 specification recommends connecting a 100 ohm resistor of at > least 0.5 W in series between each node's signal ground and the > network's ground wire, as Figure 1 shows. This way, if the ground > potentials of two nodes vary, the resistors limit the current in the > ground wire." > > Admittedly, that's defeated if local ground goes back through the power > supply, to mains earth.
So the ground, will only be usable if all the transceivers are isolated, so that the ground wire is actually a 0V network common? > Incidentally, the R9 + R12 bus bias chain is in parallel with the 120 > ohm R13, for bus termination purposes, giving under 86 ohms. (R13 = 200 > ohm would give a 120 ohm result) They're certainly biasing the bus > heavily, which is good for noisy environments. (Thanks for the link. > It's educational to see what others do.) > > Erik I was given a link to RS485.com and found that they present schematics for all the products I looked at. I found it very educational too. I didn't really want to build an adapter, but the adapters I had seen up until recently were too expensive. I have been given links to some inexpensive adapters, but now I am learning they may have deficiencies. Now the question is, do I go with what may work well enough (especially over the length of a CNC machine) or what is more technically correct. Some of the literature I have read seems to indicate that in the real RS485 world that it may be more practical to set the network up and then tune the termination, bias and etc. as needed. This RS485 thing seems to be a project in itself. Thanks for the help Erik. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending) ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
