Bus directionality fundamentals Which bus in a conventional microprocessor system is inherently bidirectional for transfers between the CPU and devices?

Introduction / Context:
Understanding which buses are uni- versus bidirectional is foundational to tracing data flow on schematics and timing diagrams. This knowledge informs buffer selection and signal integrity considerations.

Given Data / Assumptions:

• The system has separate address, data, and control buses.
• CPU reads and writes to memory and I/O devices.
• No specialized bus multiplexing or serial bus overlays are assumed.

Concept / Approach:
The address bus carries location information from CPU to devices and is therefore unidirectional. The data bus must carry information in both directions (CPU writes data out and reads data back), making it bidirectional. Control lines have defined directions; some originate at the CPU (read/write strobes), others originate at devices (interrupts), but each line itself is not bidirectional.

Step-by-Step Solution:
Identify bus roles.Address: CPU → devices only.Data: CPU ↔ devices → must be bidirectional.Control: mixed origin per signal; not a single bidirectional bus.

Verification / Alternative check:
Inspection of CPU datasheets shows separate drivers/receivers on data pins (often configured as tri-state) compared with output-only address pins.

Why Other Options Are Wrong:

• Address bus: typically one-way from CPU.
• Control bus: per-signal direction set, not “bidirectional as a bus.”
• None: incorrect because the data bus is bidirectional.

Common Pitfalls:
Confusing “shared backplane” with “bidirectional per line.” Data lines are tri-stated and arbitrated; address lines are driven by one master in most basic systems.

Final Answer:
Data bus