This disclosure describes a circuit implementation providing the functions necessary to implement an isolated I 2 C bidirectional port. The technique implements a current source as a pull up device on at least one side of the isolation system. The circuit manages and communicates bidirectional data across an isolation barrier. A method of communicating bidirectional signals and an I 2 C acknowledge (ACK) or clock stretching through an isolation channel is disclosed.
1. A communication system containing two or more communication interface devices for communicating between separate I 2 C busses, a communication interface device of the two or more communication interface devices comprising:
a current source internal to the communication interface device, the current source being connected to one of the I 2 C buses and arranged to pull the one I 2 C bus to a logic high level in the absence of an active pull down device on the one I 2 C bus;
a pull down component connected to the one I 2 C bus arranged to pull down the one I 2 C bus to a logic low level; and
a detector configured to detect when a remote communication interface device is pulling the signal level on the one I 2 C bus to a logic low level meeting the I 2 C specification at the same time as the communication interface device is pulling the signal level on the one I 2 C bus to a valid logic low meeting the I 2 C specification, wherein the detector includes a comparator arranged to compare the ratio of current in the pull down component to the total current supplied by the current source.
2. A communication interface device according to claim 1 , wherein the comparator includes a pair of inputs, wherein one of the inputs is a function of the flow of current in the pull down component and the other input is a function of the total current supplied by the current source.
3. A communication interface device according to claim 1 , wherein the one I 2 C bus includes an isolation barrier so that the two interface devices are isolated from one another.
4. A communication system of claim 1 further comprising:
a logic and storage device configured to maintain the direction of the data flow on one of the I 2 C buses based on which system pulls the signal from a logic high to a logic low first.