23.5 SEQUENTIAL LOGIC CIRCUITS

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23.5.1 Latches and Seal-in

Latches are one function built into PLCs, but there are variations.

Basically, latches allow one or more values to be frozen in time.

This circuit is a seal-in because the output locks the inputs on. After power is removed the logic will default to off.

23.5.2 Shift Registers

These allow values to be put into a `pipe-line' where values are shifted through one at a time.