Clocks, Logic Levels, Latches, etc.

I don’t write much about this level of hardware but I can’t find this info on the web using search engines—so I will write something. (This is too brief.)

Most digital electronic systems have an oscillator that produces a regular periodic two-state signal called the clock that is made available throughout the system. The signal has two voltages between which it alternates—one high and one low per period. The rest of the signals in the system carry just one useful bit of data per clock cycle.

The Latch

A latch has a data input, a clock input and a data output. (See ‘edge triggered latch’ here.) The clock signal directly controls latches by telling them just when to observe their respective inputs so as to reproduce them as outputs during the subsequent period between rising clock edges.

Outputs of many latches are combined in a few levels of logic consisting of boolean functions and these results are the inputs to the latches.

Asynchronous systems, by contrast, lack clocks.