Based on RS filp flop,the logical function of Timer 555 is discussed. When provided a voltage over 2 Ucc /3 to high flip plop terminal of Timer 555,a voltage no more Ucc /3 to terminal of it,Basic RS flip flop is set 1.

• 从基本RS触发器功能出发 ,对 5 5 5定时器的逻辑功能进行了讨论 ,认为 5 5 5集成定时器高电平触发端加小于 2Ucc/ 3的电平 ,低电平触发端加小于Ucc/ 3的电平时 ,触发器置“1”