‏What is the function of data bus , address bus , and control bus in a microcontroller ?

Suppose you wanted to implement a control unit for a computer that you are designing. A. Would you use a hardwired implementation or a micro-programmed control unit?  Why?   I would use a micro-programmed control unit for my computer. The reason for this is because micro-programmed control units are easier to handle and make modifications. Also, modern processors that utilize the CISC architecture can convert code to be more RISC-like to be used internally. B. What factors in the computer design would affect your decision?   It depends on my intended plan for the device. If I were to design a personal computer for non-commercial use, I would more than likely implement micro-programmed control units. If I were to design microprocessors for use in embedded systems or mobile devices, I would use the hardwired control unit.

Let us assume that we would like to design an ISA R-format instruction format for a processor. The processor has 256 registers and 64 opcodes. The R-format has four fields, the opcode and three fields for the registers. Show the instruction format and the bit allocation for each field.