Power-on conditioning of flip-flops Can an automatic RC (power-on) network be arranged to set a flip-flop at power-up instead of resetting it?

Introduction / Context:
Automatic RC power-on networks are frequently used to force a known state in flip-flops during system start-up. Designers often default to generating an asynchronous reset pulse, but in some applications the required initial state is a logical 1 (set). Understanding how to wire the RC network to achieve set instead of reset is practical for reliable initialization.

Given Data / Assumptions:

• Flip-flop has asynchronous SET and RESET inputs (often active-LOW).
• Power supply rises from 0 V to its nominal value.
• An RC differentiator/integrator creates a momentary pulse at power-up.

Concept / Approach:

The RC network can be connected to whichever asynchronous input establishes the desired state. If the flip-flop provides both preset (SET) and clear (RESET) inputs, connecting the RC pulse to the active-input that forces Q = 1 will “set” the device on power-up. In devices with only a reset, a small logic inverter or transistor stage can invert the pulse polarity and route it to the set input of an equivalent latch/register stage.

Step-by-Step Solution:

Verification / Alternative check:

Scope the asynchronous input at power-up to confirm a clean pulse of correct polarity and duration. Confirm via observation that the output Q starts at 1 consistently across temperature and supply ramp rates.

Why Other Options Are Wrong:

• “No” would imply RC start-up networks always reset; in reality, they can be wired to either asynchronous input, or inverted, to achieve a set condition.

Common Pitfalls:

• Pulse too narrow for the datasheet minimum asynchronous set time.
• Forgetting pull-down/up to define a DC state after the pulse ends.
• Driving beyond absolute maximum ratings during the supply ramp.

Final Answer:

yes