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Hi All Expert!!

I am designing a calculator that can key in complex number..

I connect a 4x4 Matrix Keypad and MM74C992 16 Key Encoder on PIC18F4520 microchip..

Currently I'm trying to do the programming part..

Do anybody know the flowchart??

Thanks in advance!!



It's your project, only you can design the flow chart. We will HELP you with your project if you need it, we will not do it for you.
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Well-Known Member
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.



Well-Known Member
Consider this

Besides that the old chip could be simply replaced by the micro itself, to create the flow diagram, you could try this and see how far you come:

Put in writing, yes, in writing, every single step you think is needed to make your circuit work.

You will make some mistakes, maybe, going too much into details or by the contrary, overlooking the minimal ones.

With that excercise you will start creating in your mind the base for a flow diagram.

When I start something that is completely new to me, I do just that. From there to a proper flow diagram there is not too much else to be done.

Instead of asking for it, put your efforts first.

My bet is that way you could get concrete help.
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New Member
I have to agree with TUNEDWOLF.

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. :eek:

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