Stepper motor control in HDL — why provide more than one operating mode? In a hardware description language (HDL) stepper motor design, what is the main reason for supporting multiple modes (for example, wave drive, full-step, half-step, and direction control)?

Introduction / Context:
Stepper motors advance in discrete steps by energizing stator phases in specific sequences. HDL implementations for FPGAs or CPLDs often include several modes to adapt torque, smoothness, speed range, and direction. A configurable controller lets one hardware platform serve many mechanical requirements without rewiring.

Given Data / Assumptions:

• Common mode choices: wave drive (one phase on), full-step (two phases on), and half-step (alternates one/two phases).
• Speed is set by step frequency; direction by phase sequence order.
• “Direct drive” refers to producing coil drive patterns from logic (typically via external power stages).

Concept / Approach:
Different modes trade torque and resolution. Full-step maximizes torque (two coils on), wave drive lowers power and torque (one coil on), and half-step doubles position resolution and reduces resonance. Direction control is achieved by reversing the sequence. Frequency control provides the RPM setting and acceleration ramps. Thus, exposing modes covers speed, direction, and the pattern used to energize windings.

Step-by-Step Solution:

Verification / Alternative check:
Simulation waveforms show mode-dependent coil patterns and confirm that changing the sequence order reverses direction while altering the step interval changes speed.

Why Other Options Are Wrong:

• Options a and b are each partial truths; the design usually enables both speed and direction.
• Option c alone ignores that “direct drive” still requires speed/direction control.
• Option e is unrelated to core HDL step sequencing.

Common Pitfalls:

• Driving coils directly from logic without current drivers; always use proper power stages.

Final Answer:
All of the above