The MM74C923N is a CMOS 20-Key Encoder designed by onsemi, facilitating the encoding of an array of SPST switches into a digital output. The component offers a solution for implementing a keyboard interface without the need for diodes in the switch array to prevent ghost switches. It features an on-chip logic to handle the keyboard scan, which can be driven by an external clock or capacitor. Keybounce is effectively eliminated with a single external capacitor, enhancing reliability in signal interpretation.
The device also includes on-chip pull-up devices, allowing switches with up to 50 kΩ on resistance to be used. A notable feature is its Data Available output, which signals when a valid keyboard entry is made, and its ability to remember the last key pressed even after release. The 3-STATE outputs are LPTTL compatible, providing ease of expansion and bus operation. The encoder operates over a wide supply range of 3V to 15V, making it versatile for various applications while maintaining low power consumption.
Integrated Circuits
Key encoders are integrated circuits designed to convert the press of a key or switch into a digital signal that a microcontroller or processor can understand. They are essential components in devices requiring human input through keys or buttons, such as keyboards, keypads, and custom control panels.
When selecting a key encoder, important considerations include the number of keys it can encode, its method of debounce to ensure accurate keypress detection, the electrical compatibility with the system's logic levels, and its power requirements. The MM74C923N, for instance, offers a 20-key encoding capability with built-in debounce, making it highly reliable for user input applications.
Key encoders like the MM74C923N simplify the design of input interfaces by reducing the need for complex wiring and discrete components for debounce circuits. Their ability to work over a wide voltage range and to interface directly with logic level circuits makes them versatile for various applications. Moreover, features such as the last key register and Data Available output provide additional functionality for more sophisticated input handling.
In essence, the choice of a key encoder should be guided by the specific requirements of the application, including the number of inputs, system voltage levels, desired features such as key memory, and power consumption considerations. The MM74C923N represents a robust solution for applications requiring reliable and efficient key encoding.