On 23/09/10 14:57, PICdude wrote: > Sometime years ago, I had heard (IIRC on this forum) that 1-wire > technology is patented, such that I can't implement my own slaves. > I've not come up with the patent yet, and Maxim hasn't responded to me > yet. Anyone know if this is true, if the patent is still valid, and > what the general details are? You probably couldn't find it because it wasn't applied for by Maxim. It=20 was applied for by Dallas Semiconductor: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=3DPTO2&Sect2=3DHITOFF&p=3D1= &u=3D%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=3D46&f=3DG&l=3D50&co1=3DAND&d= =3DPTXT&s1=3D%22dallas+semiconductor%22.ASNM.&OS=3DAN/%22dallas+semiconduct= or%22&RS=3DAN/%22dallas+semiconductor%22 US Patent number 6,108,751, granted August 22, 2000. PDF here: http://www.freepatentsonline.com/6108751.pdf Single wire data communication method Abstract A system architecture which provides efficient data communication, over=20 a one-wire bus, with a portable data module which does not necessarily=20 include any accurate time base whatsoever. The time base in the module=20 can be extremely crude (e.g. more than 4:1 uncertainty). An=20 open-collector architecture is used, with electrical relations defined=20 to absolutely minimize the drain on the portable module's battery. The=20 protocol has been specified so that the module never sources current to=20 the data line, but only sinks current. The protocol includes signals for=20 read; write-zero; write-one; and reset. Each one-bit transaction is=20 initiated by a falling edge from the host. The time base in the module=20 defines a delay, after which (in write mode) the module tests the data=20 state of the data line. In read mode, after a falling edge the module=20 does or does not turn on its pull-down transistor, depending on the data=20 value. Thus, the host system, after the falling edge, attempts to pull=20 the data line high again, and then tests the potential of the data line=20 to ascertain the data value. ..... Bit of a mouthful, but there you go. Won't expire for another ten=20 years, near as I can tell. > If this is not doable, I may end up rolling my own protocol that can > work with a single wire, but I'd need to know what specifically is > patented with respect to 1-Wire technology. In a word: "Everything". From the iButton MicroCan and ESD protection=20 circuitry to the 1Wire control protocol. All in that patent I linked above. I seem to recall someone from Dallas stating that they don't enforce the=20 patent with respect to 1-Wire Master devices (for obvious reasons) but=20 they will take action against anyone making slave devices that are=20 claimed to be 1-Wire compliant -- each 1-W device has a 64-bit unique=20 serial number, and Dallas didn't want S/N collisions (because this is=20 the one way to REALLY screw things up in a 1-Wire bus). IMHO there is a fair bit of prior art. If you took the signal from MSF=20 (the Rugby / Anthorn time signal), converted to baseband and sped it up,=20 you'd end up with something similar to 1-Wire. It's basically=20 pulse-width modulation. If all you've got is one wire, PWM is pretty=20 much the only game in town. If you don't claim it to be 1-Wire (call it PWM-Bus or something) and=20 don't implement some of the more esoteric bits of the protocol (i.e. use=20 it as a physical-layer with your own link-layer protocol) you might be=20 able to get away with it in the same way lots of companies got away with=20 making I2C EEPROMs... call them something else. 2-wire, MicroWire, "two=20 wire addressable serial bus"... Ob disclaimer: this is an Engineer's Opinion. Seek the advice of a=20 lawyer specialising in intellectual property law before you go designing=20 anything... --=20 Phil. piclist@philpem.me.uk http://www.philpem.me.uk/ --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .