I am going to build a very simple 2 digit calculator. I am using a 4x4 keypad for the input. I am going to use the keypad to input through the status registers on the parallel port to the PC. Then I am going to convert the data(add, subtract, multiply, or divide). Then output to two 8-segment displays. I was wondering if I need a chip to convert the data coming out of the keypad before it goes to the status register? Also, I am open for suggestions on how to do this.

 

I think what you could do is to poll the keypad from the program running on a PC to detect switch press. To poll the pad u can have 2 8 bit shift registers in which u can shift a 1 bit thru all the 16 bits over and over again and each of the bit line can be connected to the keys of the key pad. The other lines of the keys are all shorted and fid as 1 input line to the parallel port. So if u get a high line on any clock to the shift register u will know a key is pressed and the clock number will tell u the key number.

 

http://www.cs.ubc.ca/~hilpert/eec/index.html

Commodore DAC-612 Calculator Schematic

Good Luck!