Sometimes, the most difficult part when dealing with I2C is to differentiate the communication direction: which signal is sent to which device. Hence, this simple trick should be useful.
Things to notice is that:
- It only works for two devices debugging
- The hump that is caused by the resistor should not exceed the threshold of maximum VInput (ie not exceeding 0.3V for CMOS device or 0.7V for TTL device)