Bryan, you might want to check Pinnacle 52 which I developed (and at this moment am shamefully promoting :grin:).

Pinnacle 52 includes both an SPI and I2C simulation with a few I2C parts simulated. In each case, there is a window the user can open in the IDE to monitor each I2C/SPI part directly, and in the case of I2C there is actually an "I2C Monitor" window which allows the user to see the data being sent back and forth between the MCU and the I2C parts. Thus if the I2C part that the user's program is communicating with doesn't seem to be functioning as expected the user can look at the I2C Monitor window to see what data was sent and what data was returned.

In the case of Pinnacle 52, only bit-banging is supported. That's not because I don't want to or can't support direct SFR method but rather because none of the MCUs that are directly supported by the Pinnacle 52 Simulator have I2C support built-in; so with those MCUs that only way to do I2C would be to bit bang.

If you write the code for the whole I2C simulation and plan it well from the get-go then it's not hard to support both SFR-based and bit-banging access to the I2C bus. There's also no reason to support one and not the other since a well-design I2C simulation will easily support both.

Craig Steiner