On Thu, 20 Dec 2012, Charles Steinkuehler wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On 12/20/2012 3:03 PM, Kent A. Reed wrote: >> On 12/20/2012 1:56 PM, [email protected] wrote: >>> Just by chance has anyone already written the code for linuxcnc >>> to handle something like this connected to a single parallel port >>> pin http://www.adafruit.com/products/374 >>> >>> Richard >>> >> >> Richard: >> >> To quote an old movie line "Don't know nothing 'bout it." >> >> So, armed with my trusty Internet search engine, I tried to learn >> something about it. The first thing I found was this quote from an >> old Dallas Semiconductor datasheet (they're now part of Maxim >> Integrated): >> >>> NMI interrupts of the PC will not guarantee flawless >>> communication to a 1-Wire device through a parallel port >>> directly, and is discouraged to attempt. As the 1-Wire protocol >>> requires the first 15us of each time slot to contain the data >>> information, any disruption of this time segment will result in a >>> communication error. > > +1 > > I've implemented 1-wire interfaces (in hardware and on > micro-controllers), and they are timing sensitive, at least for the > identification of a 1 or zero bit (the bit-to-bit timings are pretty > loose). > > You could probably get something to work with a tuned LinuxCNC system > (no nasty latency hiccups), but you would almost certainly have to > handle a single bit in one run of the high-speed thread (meaning > busy-waits and chewing up at least the 15 uS per invocation). > > I2C is much more relaxed for timing constraints, and only uses one > more parallel port pin (3 vs. 2 for the "1-wire" bus). Note despite > the 1-Wire name, you need to parallel port pins (one output, one > input) and a transistor, fet, or diode (to make the output > open-collector) unless you've got something fancy like a Mesa card > that can do bidirectional open-collector I/O on a single pin...in > which case why are you looking at 1-Wire devices?!? :) > > While I can appreciate the money having only one signal wire saves in > things like automotive wiring harnesses, my main use for these devices > was as a unique serial number (each 1-Wire device has a guaranteed > globally unique address). Since everything was on one circuit board, > the cost for extra 'wires' to talk to an I2C temperature sensor was > inconsequential. > > <shameless plug> > BTW: I have an I2C driver available as part of my hacking LinuxCNC to > talk to a 3D printer: > > https://github.com/cdsteinkuehler/LinuxCNC-RepRap/blob/master/components/I2C.comp >
This why I ask these stupid questions before diving in Thanks, I will look more in to I2C Richard ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
