I2C over Long Distances

At the time that the I2C bus was developed, a maximum bus capacitance of 400 pF was assumed. This means that with properly designed interconnections, in theory signal transport is possible over a distance of several metres. This initially appeared to be more than adequate, but the desire to be able to cover even longer distances soon arose. For this purpose, an ‘electronic transformer’ was developed in the form of a special IC with the type designation P82B715. Using this IC makes the signal impedance a factor of ten lower, which means that the maximum distance increases by the same factor. An ‘I2C Extender’ based on this driver IC has already been described in the May 1994 issue of Elektor Electronics.