Address,data and control busses:
Microprocessor is processing device of every computing device. It is like an artificial brain. It needs to communicate with outer world. for example, It needs to communicate with Input devices to get data,it needs to communicate with memory to process data according to instructions written in memory and finally it needs to communicate with output devices to display the output on O/P devices. To communicate with external world, Microprocessor make use of buses. There are different types of buses used in Microprocessor:
It is a group of wires or lines that are used to transfer the addresses of Memory or I/O devices. It is unidirectional.In Intel 8085 microprocessor, Address bus was of 16 bits. This means that Microprocessor 8085 can transfer maximum 16 bit address which means it can address 65,536 different memory locations. This bus is multiplexed with 8 bit data bus. So the most significant bits (MSB) of address goes through Address bus (A7-A0) and LSB goes through multiplexed data bus (AD0-AD7).
As name tells that it is used to transfer data within Microprocessor and Memory/Input or Output devices. It is bidirectional as Microprocessor requires to send or receive data. The data bus also works as address bus when multiplexed with lower order address bus. Data bus is 8 Bits long. The word length of a processor depends on data bus, thats why Intel 8085 is called 8 bit Microprocessor because it have an 8 bit data bus.
Microprocessor uses control bus to process data, that is what to do with the selected memory location. Some control signals are Read, Write and Opcode fetch etc. Various operations are performed by microprocessor with the help of control bus. This is a dedicated bus, because all timing signals are generated according to control signal.