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Multiplexed AD BUS The signal lines AD0 to AD7 in 8085 microprocessor used for dual purpose. They carry address bits as well as data bits. This is called multiplexed address/data bus. This bus is used as low order address bus and data bus. The address bus and data bus are multiplexed to reduce number of pins in the IC package.

Demultiplexing of Address/Data Bus

Latch To avoid mixing up of address and data bits this must be de-multiplexed. This can be done with the help of a latch (74LS373). This bus is connected as input to the latch.

Address Latch Enable (ALE) The Address Latch Enable (ALE) signal is connected to the enable pin (G) of the latch and output control (OC) pin is grounded.

When ALE goes high, the latch is transparent and it enables lower order address bits (A0 to A7).

When ALE goes low, the latch enables lower order data bits (D0 to D7)

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