A bus system of a system on chip (SoC) includes a first and a second masters, a first slave, and a first and a second control modules. The control modules generates a first and a second access control state signals in response to a first locking access preparation request signal from a corresponding master. The access control signals are broadcasted between the first and the second control modules through a communication channel.A method of operating a bus system in a locked access mode includes allowing one of masters to access one of slaves through a control module and restricting other masters from accessing the one of slaves through other control modules connecting the other masters and the one of slaves in accordance with a control state signal.