Data Bus
The data bus is a group of eight lines used for data flow. Thses lines are bidirectional-data flow in both directions between the MPU and memory and pheripheral devices. The MPU uses the data bus to perform the second function:transferring data
The eight data lines enable the MPU to manipulated 8-bit data ranging from 00 to FF (256 numbers).
The largest number that can appear on the data bus is 11111111.The 8085 microprocessor is known as an 8-bit microprocessor.Microprocessor such as the Intel 8086,Zilog Z8000,and Motorola 68000 have 16 data lines;thus they are known as 16-bit microprocessors and the Intel 80386/486 have 32 data lines;thus they are classified as 32-bit microprocessors.
Control Bus
The control bus is comprised of various single lines that carry synchronized signals.The Bus is bidirectional but the individual line is undirectional. The MPU uses such lines to perform the third function;providing timing signals .
The term bus,in relation to the control signals,is somewhat confusing.These are not groups of lines like address or data buses,but individual lines that provide a pulse to indicate an MPU operation.The MPU generates specific control signals for every operation(such as Memory Read or I/O Write) it performs.These signals are used to identify a devices type with which the MPU intends to communicate.
To communicate with a memory-for example,to read an instruction from a memory location-the MPU places the 16-bit address on the address bus.The address on the bus is decoded by an external logic circuit,and the memory location is identified.The MPU sends a pulse called Memory Read as the control signal.The pulse activates the memory chip,and the contents of the memory location (8-bit data ) are placed on the data bus and brought inside the microprocessor.
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