john2020
Full Member level 5
Hi All
I'm looking for a keypad program in c that uses the 74c922 encoder chip. A 3x4 keypad is used. I'm really struggling with this. Can anyone help me? How do you wright the program so that the eprom can tell what keypad has been pressed according the encoder chip?
I have read the datasheet for the 74C922 here is the link,
https://www.fairchildsemi.com/ds/MM/MM74C922.pdf
You only have to supply 1 control signal to the chip, and receive 1 control signal from the chip, plus the 4 data bits that identify which key was pressed:
The DATA AVAILABLE output pin, surprisingly enough, tells you when there is data available (ie, a keypress) for you to read from the device;
The /OUTPUT ENABLE input pin enables the chip's outputs, so that you can read the data (ie, the keypress);
The A, B, C, D output pins identify which key was pressed, in accordance with the Truth Table shown on p2 of the data sheet.
But how do impliment the code to tell it to look for the data there?
And do you need a ASCII table as well? Any help would be greatly appreceated!
I'm looking for a keypad program in c that uses the 74c922 encoder chip. A 3x4 keypad is used. I'm really struggling with this. Can anyone help me? How do you wright the program so that the eprom can tell what keypad has been pressed according the encoder chip?
I have read the datasheet for the 74C922 here is the link,
https://www.fairchildsemi.com/ds/MM/MM74C922.pdf
You only have to supply 1 control signal to the chip, and receive 1 control signal from the chip, plus the 4 data bits that identify which key was pressed:
The DATA AVAILABLE output pin, surprisingly enough, tells you when there is data available (ie, a keypress) for you to read from the device;
The /OUTPUT ENABLE input pin enables the chip's outputs, so that you can read the data (ie, the keypress);
The A, B, C, D output pins identify which key was pressed, in accordance with the Truth Table shown on p2 of the data sheet.
But how do impliment the code to tell it to look for the data there?
And do you need a ASCII table as well? Any help would be greatly appreceated!