Computer Organization | Microcomputer system

The 8085 microprocessor is an example of Microcomputer System. A microprocessor system contains : two types of memory that are EPROM and R/WM, Input and Output devices and the buses that are used to link all the peripherals (memory and I/Os) to the MPU.

In 8085, we 16 address lines ranging from A0 to A15 that are used to address memory. The lower order address bus A0-A7 is used in the identification of the input and output devices. This microcomputer system has 8 data lines D0-D7 which are bidirectional and common to all the devices.

It generates four control signals: Memory Read, Memory Write, I/O Read and I/O Write and they are connected to different peripheral devices. The MPU communicates with only one peripheral at a time by enabling that peripheral through its control signal.

For example, sending a data to the output device, the MPU places the device address (or output port number) on the address bus, data on the data bus and enables the output device by using its control signal I/O Write. After that the output device display the result.

The other peripheral that are not enabled remain in a high impedance state called Tri-state. The bus drivers increases the current driving capacity of the buses, the decoder decodes the address to identify the output port, and the latch holds data output for display. These devices are called Interfacing devices. This Interfacing devices are semiconductor chips that are needed to connect peripherals to the bus system.

The block diagram of a microcomputer system is shown below:

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