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Calculator schematic circuit

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Hi guys! I must make circuit on FPGA based calculator. The calculator is by LCD 16x2 display and 4x4 membrane keypad. But i dont have idea how it will do. With VHDL code i dont have a problem, but the circuit :-?....Can anyone give me an idea how i do the circuit and help me?
 

Hi,

How many and what connections does your display have?
The same is with the keypad.

Then imagine how to detect what key is pressed.
Imagine how to display a character to the display.

Klaus
 

LCD have 16 pins, the keypad have 8 pins. I will make a Pmod module to connect them by Basys2(or Nexys 2). I suppose that Datta pins on LCD will be connected with resistors and then connected to Basys2(or Nexys 2). I think the keypad dont need resistors.
 

I suppose that Datta pins on LCD will be connected with resistors and then connected to Basys2(or Nexys 2).
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You won't generally use resistors, except for a 5V supplied LCD to help the FPGA to clamp the input voltage when reading back from data port. Besides data pins, E, RS and R/W line would be driven by the FPGA.

For the key matrix, you'll use pull-up resistor at the 4 input lines and open drain driver at the 4 output lines.
 

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