English: Diagram of a 4-phase, bundled-data communication. Top: A sender and receiver are connected by data lines, a request line, and an acknowledge line. The sender drives the data and request lines. The receiver drives the acknowledge line. Bottom: Timing diagram of a bundled data communication. From the beginning, the sender sets the data lines to their desired values. Then, the sender raises the request line to indicate that the data is valid. The receiver then raises the acknowledge line to indicate that it has received the data. The sender and receiver then sequentially return the request and acknowledge lines to their original state to complete the 4-phase communication. Outside of the time that the request line is high, the data is to be considered invalid and liable to change at anytime.