Question

What are the functions of ale and iom signals of the intel 8085a microprocessor?

Answer 1

Address Latch Enable. 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


It is a status signal. It is used to differentiate between memory locations and I/O operations. When this signal is low (IO/M = 0) it denotes the memory related operations. When this signal is high (IO/M = 1) it denotes an I/O operation.