The 555 timer integrated circuit is commonly configured in which pair of standard modes (the two classic textbook applications)?

Introduction / Context:
The ubiquitous 555 timer is a versatile analog/digital building block. Its internal comparators, flip-flop, and discharge transistor make it ideal for timing pulses and generating square waves with minimal external components.

Given Data / Assumptions:

• Standard 555 connections using the threshold, trigger, control, and discharge pins.
• We focus on the two most commonly taught and used configurations.
• External RC networks define timing.

Concept / Approach:
In monostable mode (one-shot), a trigger initiates a single output pulse whose width depends on R and C. In astable mode, the device self-oscillates, creating a square/rectangular wave with frequency and duty cycle set by two resistors and a capacitor. These are the two classic textbook modes demonstrated in most datasheets and labs.

Step-by-Step Solution:
Monostable: output HIGH for t = 1.1 * R * C after trigger; then returns LOW.Astable: charges/discharges C between 1/3 VCC and 2/3 VCC via RA and RB; period T ≈ 0.693 * (RA + 2RB) * C.Both require only a handful of passive components and no clock source.

Verification / Alternative check:
Datasheets and application notes show standard reference schematics for both modes. A bistable (latch) configuration is also possible, but less common as a primary “timer” mode compared to the two classics.

Why Other Options Are Wrong:

• Monostable, bistable: Bistable is possible, but the canonical pair is astable + monostable.
• Astable, toggled: “Toggled” is not a standard 555 timing mode name.
• Bistable, tristable: “Tristable” is not a 555 mode.

Common Pitfalls:

• Ignoring output drive limits at high frequency or large loads.
• Not decoupling the supply; the 555 can inject noise without proper bypassing.

Final Answer:
astable, monostable