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Electrical Isolation for I2C Bus

IP.com Disclosure Number: IPCOM000123661D
Original Publication Date: 1999-Feb-01
Included in the Prior Art Database: 2005-Apr-05
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Benayoun, A: AUTHOR [+3]

Abstract

Problem Description. The problem to fix: how to interconnect several machines with an I2C bus in a noisy environment, the machines having not the same ground reference.

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Electrical Isolation for I2C Bus

   Problem Description

   The problem to fix: how to interconnect several machines
with an I2C bus in a noisy environment, the machines having not the
same ground reference.

   State of the Art

   Up to now, no solutions were existing.

   Applications of the Invention

   All machines or systems willing to be connected via an
I2C bus in a noisy environment, the machines or systems having not
the same ground reference.

   Description of the Invention

   The electrical isolation is based upon optocouplers.  When
no data are transmitted, the SDA (data) line is in its idle state 5
volts on both sides A and B.  When a 0 volts (active level) is
applied, for example, on the A side, the optocoupler O2 is turned
"on", and we can find 0 volts on the anode of the optocoupler O1,
and thanks to the diode D1, SDA-B reaches also the level 0 volts.  On
the A side, D2 is used to "shunt" the input of the optocoupler O2 in
order to avoid a memory effect of the level 0 on the A side.  When we
apply 0 volts on the B side , it works in a symmetrical manner.  The
SCL lead (clock) should have the same logic as SDA.  We can connect
up to 6 devices at 100Khz.  If more devices are connected, the
capacitance will be too high.