8-bit AVR Microcontrollers

Multi-Master Systems and Arbitration

If multiple masters are connected to the same bus, transmissions may be initiated simultaneously by one or more of them. The TWI standard ensures that such situations are handled in such a way that one of the masters will be allowed to proceed with the transfer, and that no data will be lost in the process. An example of an arbitration situation is depicted below, where two masters are trying to transmit data to a slave receiver.

Figure 1. An Arbitration Example

Several different scenarios may arise during arbitration, as described below:

This is summarized in the next figure. Possible status values are given in circles.

Figure 2. Possible Status Codes Caused by Arbitration