It would be better to use an EEPROM, but I already had some UV erasable EPROM's.
Step 1: Parts
-An EPROM (in my case a M2732A-4FI)
-LEDs and resistors for them
-A 5V power supply
-Bread Board or any other board
-if you want, you can add switches
Step 2: Schematic
Step 3: Operating It
The leds show you the written bits.
Step 4: Programming
I need some ideas from where to get 21V, that are needed for programming.
And some ideas on how to select the address that it will write to. I need 12 bits for selection + 8 data bits.