peripheral circuit functions built-in to the HC12 microcontroller, that are not part of the CPU itself or the memories. Access to these is via external pins on the Microcontroller IC package. What are some of these built-in circuit functions called, and what do they do? Solution The peripheral circuit communicate with the Microcontroller using built in cirucit called BUS. The bus is a set of shared communication lines that serves as the central nervous system of the computer. Data, address, and control signals are shared by all system components via the bus. Each component connected to the bus communicates information to and from the bus via its own bus controller. The data lines,address lines, and control lines allow a specific component to access data addressed to that component. The data lines are used to communicate words to and from data. registers in the various system components such as memory, CPU, and input/output (I/O) peripherals. The address lines are used to select devices on the bus or specific data locations within memory. Devices usually have a combinational logic address decoder circuit that identifies the address code and activates the device..