Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Unless there is particularly good reason for you to use a seperate key encoder chip, I would dump it in favour of some firmware in the micro. Saves on cost, board complexity and will lighten the power requirements too.
I am having extra grief with my own project because I am using a dedicated keypad decoder chip. ( 74HC922).
In theory, using it saves writing a debouncing and decoding routine in your code, but you then have to write a routine to detect the "data valid" signal and act on it, plus that chip does not provide a logical binary output for the pressed key, which means that you have to write a routine that translates the output from the chip into something usefull for your program.
I think that those decoder chips were designed with discrete logic circuits in mind, as they have been around for a long time and are on the verge of being dis-continued, I believe. ( Another reason to decode and translate your keypresses in software.) You don't want to design a device with parts that are not going to be available in future.
Now I just have to listen to my own advice.