Marc, Vince You can wire a network anyway you want of course, but I suggest you look at the 1WRJ45 wiring standard as being the most compatible with the largest number of manufactures and boards out there. You can find the original proposal document on www.1wire.org in the standards section.
In summary it is: Pin 1 - VCC_RTN (5Volt regulated Return) Pin 2 - VCC_PWR (5Volt regulated source) Pin 3 - A_RTN (Aux signal return) Pin 4 - OWIO (1-Wire data signal) Pin 5 - OWRTN (1-Wire data return) Pin 6 - A_Sig (Aux signal - meant for slow signal rates) Pin 7 - VRAW_PWR (+12 Volt regulated power source) Pin 8 - VRAW_RTN (+12 Volt regulated power return) Note this is different than the document from hobby boards in that the VRAW is set to +12 limit not 24 volts (Anything greater than about +14 volts will cause catastrophic failures or problems on some manufactures boards! Which was the reason why a +12 Volts regulated voltage was originally selected. Besides there aren't any boards that need more than +12 Volts regulated that I am aware of...and you really don't want to use this power source for relays and the like anyway...its bad practice. Considerable thought and discussions took place many years ago in the creating of the 1WRJ45 standard and I wish everyone would stick to it, or at least discuss why it should be changed (grumble moan...) There were discussions about using higher voltages for power delivery (including POE), but since it conflicted with existing boards and would require DC-DC converters on the boards this was dropped. 1-Wire signals have very little noise immunity inherently, so adding sources of noise next to the signal is a bad idea in general. Crosstalk can be an issue. You are much better off running separate cables for power (for high powered units like relays, motors and the like and using a shielded cable for these sources. Use unshielded for 1-wire signals since the added capacitance of a shield can be a problem. The Aux signal lines were originally thought of as having slow signal rates for this reason and are good for times you need to put switch closure type of stuff onto the cable. So if you wanted to try to loop the 1-wire signals back through the cable I would recommend this pair be used, though you will conflict with some 1-Wire devices being made (which can put +5 Volts out on them). In general I do not recommend this practice as you increase the likely hood of creating a marginal system. (People have done it though and it can work). Where in the cable the signal wavefront through the cables will cross will depend on cable length etc... so it is almost impossible to predict signal reflection issues, etc. I've discussed this issue with engineers at Dallas and others and the consensus was that it is a bad idea and not worth the bother. You are better off using a separate cable to return or use a switched branch for the device. And the cost of the extra CAT cable is insignificant to the potential problems you can see in a single cable looped system IMO. A design issue I have been struggling with for the past year or so is the issue of 1-Wire power management, ie. What happens or should happen when there is a power short or a cable end gets dropped in water etc. or what power control over the cable power should there be.. .but that's another issue. Anyway always glad to discuss any of this off line... what's most important is to select a cable standard and stick to it for all your 1-wire devices. BTW, powered temp sensors can perform faster than parasitic ones... Cheers, David Lissiuk ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Owfs-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/owfs-developers
