I have two chips that are connected using two lines. One appears to be the clock line (50% duty cycle), but it doesn't have to be (sometimes constant high). The other line appears to be totally random, but still digital. It might be data.
There is a third line between the chips, but it appears to be for something else - it's on a way slower speed and is on another place on the PCB. It also doesn't use a pull-up, while the other two do.
How can I find out what protocol (I2C, SPI, RS232, ...) is being used on the lines, if any standard?