Alright, let's dive into the technical swamp of logic circuits, where the term "active low" lurks. Active low is the equivalent of writing your name in binary, but with an inverse twist. Definition "Active low" refers to a signal or condition in a digital circuit that is activated or asserted when it is at a low voltage level, typically close to 0 volts, and deactivated when it is at a high voltage level, typically close to the supply voltage (like 5V or 3.3V). This means a logic level '0' triggers the action. Why Use Active Low? Historical Reasons: Early TTL (Transistor-Transistor Logic) circuits had better noise margins and power consumption characteristics when pulling signals low rather than high. Power Consumption: In many circuits, driving a line low consumes less power. Circuit Design: Sometimes it simplifies the design, especially with open-collector/open-drain outputs that can only sink current (pull the line low). How It's Noted Active low signals are typically indicated with a bar or a slash over the signal name, like RESET ‾ RESET or / 𝑅 𝐸 𝑆 𝐸 𝑇 /RESET, or an asterisk suffix, like RESET*. Examples in Action Reset Pins: Most reset pins on microcontrollers and other ICs are active low. This means pulling the reset pin to ground (0V) will reset the device. Chip Selects: Many memory devices use active low chip select signals ( CS ‾ CS ) to enable or disable the chip. Interrupts: Interrupt lines ( INT ‾ INT ) are often active low, meaning an interrupt is triggered when the line is pulled low. Active Low Truth Table Here's a quick truth table to illustrate the concept: lua Copy code Signal | Meaning ----------|-------------------- 0 | Activated (true) 1 | Deactivated (false) Practical Example Imagine a doorbell circuit designed to sound an alarm when the door is opened: Sensor Signal (Active Low): When the door is closed, the signal is high (1). When the door is opened, the signal goes low (0), triggering the alarm. Active Low vs. Active High To crystallize your understanding, let's juxtapose: Active High: Action occurs when the signal is high (1). Active Low: Action occurs when the signal is low (0). So, in essence, "active low" is your circuit's way of whispering "do something" when the voltage level drops. It's a nifty inversion that keeps designers on their toes and circuits running efficiently.