Active low意思

"Active low" is a term used in electronics and logic circuits to describe a signal or condition where a low voltage level represents an active or asserted state, while a high voltage level represents an inactive or de-asserted state. In other words, the circuit operates when the signal is low, not when it is high.

This is in contrast to the more common "active high" configuration, where a high voltage level indicates an active state, and a low voltage level indicates an inactive state.

The terms "active low" and "active high" are often used in the context of inputs and outputs of integrated circuits, such as logic gates, microcontrollers, and other digital devices. For example, an input that is active low would require a low voltage level to be asserted, while an output that is active low would produce a low voltage level to indicate that it is on or in an active state.

The specific voltage levels that are considered high or low can vary depending on the technology and the device in question. For example, in TTL (Transistor-Transistor Logic) circuits, a voltage level of 2.4 volts or less is considered low, while a voltage level of 2.4 volts or more is considered high. In CMOS (Complementary Metal-Oxide-Semiconductor) circuits, the threshold voltages can be different, and the levels can be positive or negative depending on the type of device.