Source and Dest mac address of BPDU during STP initial convergence

Hi,

Sw_A----------Sw_B-----------Sw_C

STP initial convergence.

Consider Sw_A is root bridge. During initial convergence, Sw_A is elected as Root Bridge, Now What is the Src and Dst mac-address of the BDPU that SW_A sends?? SW_B will forward the same BPDU to Sw_C, in this case what is the Src and Dst mac-address??

Please help me on this.

Thanks.