Clock Circuits

Although the concept of a totally accessible system represents an ideal situation for users, designers now must limit access toand conceal code sequences forsoftware routines for calibration, diagnostics, memory erasure, system reset, and more. In a system that includes a computer-compatible interface, such as an RS-232, a GPIB, or an infrared-I/O port, the system`s software can detect unique input patterns and execute the "secret" code sequences...

This Design Idea describes an inexpensive circuit to generate two extremely high-quality, crystal-clock-reference-signals, one of which is a PWM-controlled VCXO (voltage-controlled crystal oscillator) clock signal (Figure 1)...

As a followup to my VCR Pong project, here is a gadget that is actually useful in the Real World! It superimposes the time of day, in "HH MM SS" format, in the bottom right-hand corner of an existing video signal. My friend Scott uses it with his home security system...