Microprocessor buses: is an address bus typically unidirectional (from CPU to memory/IO) because only the processor drives physical addresses?

Introduction / Context:
A basic microprocessor system uses three bus types: address, data, and control. Understanding their directions clarifies how components communicate. This question checks whether the address bus is rightly termed “unidirectional.”

Given Data / Assumptions:

• Conventional CPU-connected memory or peripherals (no exotic bus bridges).
• Address lines A[n:0] are driven by the CPU to specify a location.
• Data bus allows reading or writing actual data values.
• Control bus conveys signals such as RD, WR, IO/M, CS.

Concept / Approach:
Only the CPU (or a current bus master like a DMA controller when bus-mastering) asserts the physical address that selects a memory or IO location. Thus, from the CPU’s perspective, address lines are driven outward; memory devices do not drive addresses back to the CPU. Hence, the address bus is termed unidirectional. Even when DMA masters take control, they become the driver; the bus still carries addresses in one direction from the current master to the slaves.

Step-by-Step Solution:

Verification / Alternative check:
CPU pin descriptions show address pins as outputs, while data pins are typically bidirectional.

Why Other Options Are Wrong:
Does not apply: denies standard bus directionality. “Only if DMA is disabled” or “only Harvard” add conditions that do not alter the basic definition.

Common Pitfalls:
Confusing bus arbitration (who drives) with signal direction on a given transaction; assuming address echoing can occur from memory (it does not).

Final Answer:
Applies