The 555 is one of the most popular integrated circuits (ICs) ever made. When you use it, you need to be aware of the purpose of each of the eight pins in the 555 package. You may also occasionally use a 556 IC, which consists of two 555 timers in a single package, and the same applies to knowing its pinouts as well.

Function 555 Timer 556 First Timer 556 Second Timer
Ground 1 7 7
Trigger 2 6 8
Output 3 5 9
Reset 4 4 10
Control voltage 5 3 11
Threshold 6 2 12
Discharge 7 1 13
Vcc 8 14 14