8051 External EPROM Interfacing — Demultiplexing Requirement When interfacing an external EPROM to an 8051, it is necessary to demultiplex the address/data lines (AD0–AD7) from Port 0. State whether this requirement is true or false.

Introduction / Context:
The 8051 saves pins by multiplexing the low address byte and data on Port 0. External memories like EPROM require a stable address while data is read, which demands demultiplexing with a latch controlled by ALE.

Given Data / Assumptions:

• P0 = AD0–AD7 is time multiplexed.
• ALE provides an address latch enable pulse each external cycle.
• Typical latch parts are 74HC373 or 74HC573.

Concept / Approach:
During the first phase of the cycle, P0 carries A0–A7 and ALE is high. A transparent latch captures the address. When ALE goes low, P0 switches to data D0–D7 while the latched address remains at the memory pins. Without demultiplexing, the EPROM would see address corruption when the bus turns to data.

Step-by-Step Solution:
1) Use ALE to clock the low address into the latch.2) Hold the latched address on the memory A0–A7 pins.3) Allow P0 to drive data lines without disturbing the address.

Verification / Alternative check:
Refer to standard 8051 memory interface diagrams showing P0 through a latch to memory address lines and P2 directly to high address lines.

Why Other Options Are Wrong:

• False: Ignores the multiplexed nature of P0.
• Only necessary above 8 KB: Size does not change the bus requirement.
• Not required if Port 2 is unused: Port 2 handles high address bits; it does not eliminate the need to separate A0–A7 from D0–D7.

Common Pitfalls:
Connecting P0 directly to memory address and data without a latch; forgetting to tie ALE to the latch enable.

Final Answer:
True