Path: utzoo!attcan!uunet!mcvax!ukc!dcl-cs!nott-cs!ucl-cs!Bill From: Bill@ucl-cs.UUCP Newsgroups: sci.electronics Subject: Re: I2C Bus Message-ID: <109@ucl-cs.UUCP> Date: 8 Dec 88 11:52:11 GMT Sender: william@ucl-cs.UUCP Lines: 46 Yep, I used an I2C bus system about 3 yrs ago, so my recollection is a little vague, but it is a 3-wire serial data protocol with an arbitration system. The three lines were CLOCK, DATA, and you could have at least one MASTER device, and several SLAVE devices. We used only one master, so I never investigated the multimaster facility (if it existed!), and the protocol consists of the master looking at the lines to see if they are floating, and if they are it asserts an address which corresponds to a particular slave (slaves have the address hardwired in). If the slave needs data, then this is sent too. The clock is used to synchronise the data. Then the slave can reply with some response. The data speed goes up to about 500Kbits/s, I think. The maximum length of the bus line should not exceed about 2 metres or so because signals are asserted as LOW=0V, HIGH=Floating->5V. This is intended as a VERY ROUGH GUIDE!!! The information above should all be checked up - I did not design any I2C stuff, I just sent addresses and data to the I2C software that another guy wrote. The master, in our case, was a 6303 processor and the I2C was controlled by some general I/O lines. We used it to run a Mullard teletext controller/acquisition chip and a TV tuner chip - I forget the numbers. POINTS TO NOTE: The I2C protocol driver for one master was written in under a day, so it isn't too difficult. All device types that are used on the I2C bus will have a unique address code, which is shown in the data book for the device. Some (all?) also have another address, selectable by a pin, which can be used if you want two devices on the bus. Hope this is of some help, sorry I cannot recall more, but I don't have any of the design sheets anymore. Have fun! ... Bill ************************************************************************ Bill Witts, CS Dept. * Nel Mezzo del cammin di nostra vita UCL, London, Errrp * mi ritrovai per una selva oscura william@cs.ucl.ac.uk * che la diritta via era smarrita. ************************************************************************