BUS STRUCTUR
1)Data Bus:
Data bus provides the path for monitoring
data between the system modules. The data bus is a group of 8 lines used for
data flow. The bus has various numbers of separate lines like 8, 16, 32, or 64.
Which referred as the width of data bus . It is bidirectional i.e data flow in
both direction between the microprocessor unit and memory as well as peripheral
devices. The microprocessor use data bus to perform transferring data and
binary information.
2. Address Bus:
It is a group of 16 lines generally identified as A0 to A15. It is
unidirectional i.e bits flow in one direction only from MPU to peripheral
devices. Each Lines of address bus are used to designate the source or
destination of the data on data bus. For example, if the CPU requires reading a
word (8, 16, 32) bits of data from memory, it puts the address of desired word
on address bus. The address bus is also used to address I/O ports. Bus width
determines the total memory the up can handle.
3. Control Bus:
The control bus is comprised of various single lines that carries synchronization signal. The microprocessor unit uses such line to perform the timing signal. The control bus has the individual lines that provide a pulse to indicate the microprocessor unit operations. The control bus is a group of lines used to control the access to control signals and the use of the data and address bus.
The control signals transmit both command and timing information between the system modules. The timing signals indicate the validity of data and address information, where as command signals specify operations to be performed.
Some of the control signals are:
- Memory Write (MEMW): It causes data on the bus to be loaded in to the address location.
- Memory Read (MEMR): It causes data from the addressed location to be placed on the data bus .
- I/O Write (IOW): It causes the data on the bus to be output to the addressed I/O port.
Fig. The 8085 bus structure
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