1. APB bridge 
The bridge unit converts system bus transfers into APB transfers and performs the following functions:
• Latches the address and holds it valid throughout the transfer.
• Decodes the address and generates a peripheral select, PSELx. Only one select signal can be active during a transfer.
• Drives the data onto the APB for a write transfer.
• Drives the APB data onto the system bus for a read transfer.
• Generates a timing strobe, PENABLE, for the transfer.