SCL SCL input or output value SDA SDA input or output value SCL DDR SCL data direction register value SDA DDR SDA data direction register value link state current state of LINK state machine pcol state current state of PCOL state machine in data register used by link state machine to hold data currently being assembled from SDA out data register used by link state machine to hold data currently being pumped out through SDA cmd register used by pcol state machine to hold current command p0 register used by pcol state machine to hold parameter 0 of current command p1 register used by pcol state machine to hold parameter 1 of current command p2 register used by pcol state machine to hold parameter 2 of current command