Active high意思

"Active high" is a term used in electronics and digital circuits to describe the behavior of a logic signal or input/output (I/O) pin on a device. In this context, "active" refers to the state that is considered to be the functional or operational state, and "high" refers to a voltage level that is greater than a certain threshold value.

In most digital systems, there are two primary voltage levels used to represent the binary states of 1 (high) and 0 (low). The "high" state is typically associated with a voltage that is close to the supply voltage (Vcc), while the "low" state is typically close to ground (0V).

An active high signal is one where the "high" state is the active or functional state. This means that when the signal is at the high voltage level, it is considered to be on, enabled, or true. Conversely, when the signal is at the low voltage level, it is considered to be off, disabled, or false.

For example, in a TTL (Transistor-Transistor Logic) circuit, the active high state might be around 2.4 volts or higher, while a voltage below 0.8 volts would be considered a low, or inactive, state. In CMOS circuits, the active high level is often Vcc, and the low level is 0V.

The opposite of active high is "active low," where the low state is the active or functional state. Active low signals are less common than active high signals but are used in certain applications, such as reset lines or inputs that are inverted by default.

The term "active high" is also used in the context of input or output pins on integrated circuits (ICs), such as microcontrollers or digital logic chips. For example, an output pin might be described as active high if it outputs a high voltage when it is enabled and driving a signal. An input pin might be active high if the device interprets a high voltage on that pin as an asserted or true input condition.

In summary, "active high" is a term that describes the functional state of a digital signal or pin when it is at a high voltage level, indicating an enabled, on, or true condition.