In this application, two 2-input NAND gates are used to create an active-low SR latch as shown in Figure 9-1. The two additional gates can be used for a second SR latch, or the inputs can be grounded and both channels left unused.

The CD74HC30 is used to drive the tamper indicator LED and provide one bit of data to the system controller. When the tamper switch outputs LOW, the output Q becomes HIGH. This output remains HIGH until the system controller addresses the event and sends a LOW signal to the R input which returns the Q output back to LOW.