Found in an ancient American documentation, this circuit can generate signals up to 40 MHz for a Z80, microcontroller widely used at the time. The circuit must be powered with 5 V and also serves as a shield.
This setting appears with variations at various points on this site. This is from a Motorola...
This circuit indicates through LEDs when an automotive fuse is open. ...
The circuit shown in the figure generates a rectangular signal whose frequency depends on C1. For...