Hi Let me add my two cents once again here about sharing 1-wire and other protocols. The bottom line is don't. While it's possible in some cases to get it to work you increase the chances of problems with your 1-wire network. And the problems you see will be nearly impossible to troubleshoot and may show up as early part failures, unexplained errors and retries and the like, that seem to change with the every change of the weather or day. CAT cabling is cheap when considered against the troubles you may cause.
The typical 1-wire slave device is specified with a VIH (guaranteed high state) of 2.2 volts and a VIL (guaranteed low state) max of .8 volts. This is the transition area in which the logic state is undefined for the slave. (What the slave sees is really the critical thing in a 1-wire system and in some ways the hardest thing to control due to cable effects). With an active pull-up being triggered at .95 volts (as in the DS2480B) there is not much margin for error. And with a cable impedance match of 100 ohms for the CAT5/6 cable and a typical bus master weak pull-up of 4 ma it pulls the low to about .4volts typically. So you are left with about .4 volts working range for a low signal best case. Now if you consider the signal cable integrity effects of the 1-wire signals over a transmission line (which a typical 1-wire net is), the end effects can be quite startling due to the mis-matched slave impedances. Simulations and real life measurements have shown that you can see as much as .5volts overshoot/undershoot also (clamped with BAT54S at the slave device) which may be near the slaves max limits to handle in some situations. And you have to consider both the near and far end cable effects since your slaves may be distributed throughout the cables length. The actual effects depends on sensor placements, loads, slew rates, cable length and other numerous things but the end effect is that it can push the working range of the signal very hard depending on the system. Add in the effects of hubs which lower the noise floor and you can see you really very little if any at all to work with (depending of network design). So ANY noise source (be it from crosstalk from an unregulated supply ripple or signals like Ethernet can easily push the 1-wire over the edge. And any of these reasons can show up as unexplained and interment errors on the 1-wire network. I especially don't like unregulated supplies in the cable in particular, since they can cause problems due to coupling to power line transients and suffer from wide voltage ranges depending on load, and the quality and wide tolerances and differences between manufactures of the transformer and basic filtering in the supplies (Among other reasons). Much better to use a regulated supply as they only cost a dollar or two more over an unregulated supply and you generally only need one. And I also prefer linear regulation (IMO) since they are cleaner and typically better regulated than switching supplies. But either form of regulated supply should work. Heavy use of BAT54's is also recommended to help clamp signals at the sensors to the supply rails. The 1-wire protocol is surprising in that it can work due the relaxed nature of its timing over a considerable range. But don't push it. Keep to linear networks, use a good bus master (like the LINK), use lots of protection throughout the network (BAT54s typically), and don't mix other signals with your 1-wire cable. (Or at worst use good clean regulated supplies in the cable if you must like the 1WRJ45 standard allows). Don't mix multiple 1-wire networks into the cable and don't double back the 1-wire signal through the same cable. Use the Dallas RJ12 or 1WRJ45 wiring standard (both available on www.1wire.org for your wiring standards). If you follow these simple rules things should work fairly well and be fairly reliable. Note people have made all sorts of networks work, but they tend to be unreliable or limited in range etc., and not at all worth the troubles they can cause. Cat5E cable is cheap compared to your time spent trying to find a problem. If you need to run another protocol, run it in its own cable at least from the 1-wire network. Hope this helps, Cheer David Lissiuk ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Owfs-developers mailing list Owfs-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/owfs-developers
