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A PS2 Keyboard Input FPGA Code with an LCD Output Display.
This circuit example extends the capability of our previously described PS2 Keyboard input port. Here we display the PS2 pressed key directly on a 1602 LCD display. You should look at the LCD Display FPGA code before going further.

There are no hardware changes to the board if you already have the PS2 keyboard port and 1602 LCD installed and working.
Interfacing the PS2 module to the LCD display module is very simple.   Here is a picture of the code in action.
    FPGA_Keyboard Live
Here is the core FPGA code.
    FPGA_PS2_LCD Circuit
A few things to keep in mind.  First remember that the 1602 LCD display first needs to be initialized by sending it a few data bytes before it is operational.  We do this with its "
RS" pin low. Sending each byte by pulsing its "EN" pin.  These signals come across on the LCD_INIT_DATA_BUS[7..0] and arrive on the actual LCD pins through the 2:1 MUXs, the MUX_Switch being HIGH. When the initialization is done the MUX_Switch goes from high to low.  The data then going to the LCD display comes from the PS2 keyboard via KB_DATA_OUT[6..0]
    FPGA_Keyboard circuit

It's quite impressive that with a few simple diagrams and a few wires how sophisticated a circuit one can draw with these FPGAs!  
To do this is 74LSxxx hardware with or without a CPU would take a far larger effort.

Again this is a very simple example of using our Cyclone IV to interface a PS2 keyboard with a LCD display.  Please study the files below to understand completely what is going on.

There is a minor bug in the program in that if you reinitilize the LCD display (ie. upload the code again) without a power down the LCD display gets confused. (More code needs to be added to reset the LCD upon reset).

PS2_LCD.ZIP  (V1.0 10/18/2018)

This page was last modified on 11/04/2018