The oscillator in Figure 1 has several desirable features. You can adjust the oscillator frequency from approximately 500 kHz to 4 MHz, it is fairly stable for an RC type, and it uses inexpensive standard components. Also, you can easily control the oscillator using a µP or other standard logic.

Gates IC_1B, IC_1C, and IC_1D comprise the classic oscillator that you find in most data-book application notes. This design adds the feedback from the output of IC_1B to the input of IC_1A. The ballpark formula for oscillation is as follows:

R₂ limits the maximum frequency when R₃=0.

When OSC ENABLE goes low, the circuit oscillates instantly at frequency. The width of the first pulse is very close to the succeeding pulses because of the presence of the 1N4148 diode. Other diode types will cause the width of the first pulse to be different than succeeding ones. When OSC ENABLE returns high, the circuit completes the current output pulse before stopping. Thus, the oscillator turn-off is synchronous even though the OSC ENABLE signal is asynchronous. You can use almost any logic family for IC₁, but the frequency range will vary depending on the family you use. (DI #1869)