A bus system is provided. The bus system includes a master device and a plurality of slave devices electrically connected to the master device. Each slave device has an alert handshake pin. The alert handshake pins of the slave devices are electrically connected together via an alert handshake control line. When the alert handshake control line is at a first voltage level and a first slave device want to communicate with the master device, the first slave device controls the alert handshake control line to a second voltage level via the alert handshake pin, such that the slave devices enter a synchronization stage. Among phases of each assignment period, in a first phase corresponding to the first slave device, the first slave device controls the alert handshake control line to the second voltage level via the alert handshake pin.