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4x4 keypad interfacing microcontroller PIC18F4520

zZzZ_zzZ

New Member
Hi! I am currently doing a security alarm project in school and I need help with the coding. I am using 74C922 and I have no idea how to code it. How do I scan the keypad when the output of 74C922 is A, B, C, D ? How do I indicate the 0000 = '1' , 0001 = '2' , 0010 = '3' , 0011 = 'F'........ ? Please help ;-;
 

zZzZ_zzZ

New Member
If you want to use the 74C922, then consult it's datasheet - but don't you have enough spare pins on the PIC to do it directly?.
It is part of the assignment and all the components are soldered on the project board so I am not able to remove the 74C922. All I need to do is the coding part which I do not know how :(
 
Last edited:

zZzZ_zzZ

New Member
Then consult the datasheet, getting people to do your work for you teaches you nothing.
I am not getting people to do my work tho, I just need some help like an explanation. I know the scanning of the keypad but not when the 74C922 is connected to the keypad. The data sheet did not mention anything about the outputs so it’s not helping me. Thanks for replying tho
 

Visitor

Active Member
Searching for 74C922 provides this image. The chip handles the dirty work of scanning the keypad, and provides 4 output bits A-D. The key pressed is presented as a 4-bit binary number.

The fifth pin to be aware of is the DATA AVAILABLE pin. When this pin is high(or maybe low? - check the data sheet), the state of A – D should indicate which button is pressed.

Read the data sheet to understand the exact sequence of events. This is a little help to get you started.example-74c922-so.jpg
 

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