AN-426 Datasheet (Altera) - Analog Keyboard Encoder

AN-426, Analog Keyboard Encoder

www.datasheet4u.com Using MAX II CPLDs as Analog Keyboard Encoders Application Note 426 July 2006, Version 1.0 Introduction Keyboard encoders are a very common application for CPLDs.

Typically a processor, ASSP, or ASIC does not have enough pins for keypads or keyboards.

I/O expansion is a very common function for CPLDs and allows a processor to decode a very large keyboard with very few I/Os.

Even though CPLDs like MAX® and MAX® II may have abundant low-cost I/Os, decoding a keypad or keybo

AN-426 Features

* ust be strong enough when switch 1 is shorted, as shown in Equation 3. (3) ( VCC

* V OL )

* -R 1 < I OL Resistor stack R1-R5 and capacitor C1 forms an RC tim