The operation of a microprocessor unit includes,
- Memory Read.
- Memory Write.
- I/O Read.
- I/O Write.
Communication of a Microprocessor unit with peripheral devices involves,
- Identify peripheral or memory location.
- Transfer data and instruction.
- Provide timing and synchronization signals.
The microprocessor uses three sets of communication lines called buses to perform these functions. A bus is a collection of lines, which perform the same logical task. The 8085 bus organization is shown in the figure.
- Group of 16 bits from A0 to A15.
- Carries the address of a particular location.
- Unidirectional– Data flows from microprocessor to peripheral devices only.
- Function– To identify a peripheral or a memory location.
- Capable of addressing 65536(216) memory locations. (Generally 64K)
- Group of 8 lines used for data flow.
- Carries the data to be transfered.
- Bidirectional– Data flow in both direction between the microprocessor and memory / peripheral devices.
- Function– To transfer binary data and instruction.
- Enable the microprocessor to manipulate 8-bit data ranging from 00 to FF. (28=255)
- Group of various single lines that carry control signals.
- Microprocessor generate specific control signals for every operation.
- Function– To provide timing and synchronization signals.