Bus and Cycles in microcontroller

BUS: Bus is a group of conducting wires or paths used to carry the information in form of digital signals.
ADDRESS BUS: This is a bus used to carry the address of memory or I/O device from the CPU,it is unidirectional.
DATA BUS: This is the bus used to carry the data between the CPU and memory or I/O device, it is bidirectional.
CONTROL BUS: This is a bus used to carry the control signals between CPU and memory or I/O devices.
FETCH CYCLE: It is a fixed time period taken by the CPU to fetch the opcode of an instruction from the memory. In the fetch cycle, the CPU places address present in program counter on the address bus and sends it to the memory in one T-state. In the next T-states, it gets the opcode of the instruction from the memory. The total time for sending address and getting data is called Fetch cycle.
EXECUTE CYCLE: It is the time required to decode and execute an instruction.the instruction decoder decodes the opcode of the instruction. The timing and control unit generates required timing and synchronising signals for execution and the instruction will be executed.
INSTRUCTION CYCLE: It is the time required to complete the fetching and executing an instruction is called instruction cycle.
INSTRUCTION CYCLE = FETCH CYCLE + EXECUTE CYCLE.