What is ALE? Explain the functions of ALE in 8085.

Answer Posted / k. k. ghosh

8085 processor has 16 address lines for 16 bit address of a
memory location. Out of this 16 address lines 8 adress
lines are solely dedicated to transfer 8 higher order
address bits while the remaining lower order 8 bits of the
address are sent through another 8 lines multiplexed with
the 8 bit data lines. It is the control signal ALE to be
sent by the processor in appropriate time to indicate the
operation of this 8 bit multiplexed bus whether it will be
used to send the lower order 8 address bits or to send the
8 data bits. How it is indicated ? Making ALE control HIGH
the multiplexed 8 bit bus will act as address bus while
making ALE control LOW the same 8 bit multiplexed bus will
act as data bus. Thus, ALE = 1 makes the address latched
i.e. latch enable and ALE = 0 makes the adress bus disable
but making it data bus enable. In this sense, this 8 bit
bus better should be said as data bus.

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