Explain how the address and data information is separated on the address data pins of 8085 microprocessor during the instruction fetch and execution s

Question

**Explain** how the address and data information is separated on the address data pins of 8085 microprocessor during the instruction fetch and execution stages.

Accepted Answer

**Address/Data Separation on 8085**

8085 has multiplexed AD7-AD0 (low address + data) to save pins.

**Mechanism:**
- **T1 of machine cycle:** ALE (Address Latch Enable) high → AD7-AD0 carries **A7-A0**. External latch (74LS373) captures it when ALE falls. A15-A8 already stable on high bus.
- **T2-T3:** ALE low → AD7-AD0 now becomes **D7-D0** bidirectional data bus for read/write. Control signals IO/M, RD, WR determine direction.
- **Demultiplexing:** ALE→LE of 74LS373 latches address; after that data flows.

Thus address and data share pins time-multiplexed, separated by ALE timing, enabling 16-bit address with 8-bit data on 40-pin package. Equivalent in 8051 Port0 behaves similarly.

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