555 timer operating modes: The popular 555 timer integrated circuit can be configured in multiple modes. In basic usage, it supports astable (free-running oscillator) and monostable (one-shot) operation with simple external components. Judge the statement.

Introduction / Context:
The 555 timer is a staple of timing and waveform-generation circuits. Its internal comparators, flip-flop, and discharge transistor allow flexible configurations with just resistors and capacitors, making it ideal for lab and product prototyping.

Given Data / Assumptions:

• Standard bipolar or CMOS 555 timer.
• External R, C components define timing.
• Common configurations: astable and monostable (and also bistable with suitable wiring).

Concept / Approach:
In astable mode, the 555 charges and discharges the capacitor between threshold levels, producing a continuous square/rectangular wave. In monostable mode, a trigger edge initiates a single pulse of defined width, after which the output returns to its stable state. Both configurations are documented and widely used.

Step-by-Step Solution:

Verification / Alternative check:
Reference application notes: both modes are standard, with equations for frequency, duty cycle, and pulse width based on R and C values.

Why Other Options Are Wrong:

• Incorrect / Only astable / Only monostable: Contradict numerous canonical application circuits.
• Requires external microcontroller: Not required; 555 is self-contained with passive components.

Common Pitfalls:
Forgetting trigger polarity in monostable mode; ignoring reset pin behavior; miscalculating duty cycle in astable without diode steering for duty correction.

Final Answer:
Correct