you can make a rom by using NOT gates for 1s and empty outputs for 0, if you want it to be 1 value permanently.
Viewing post in Digital Logic Sim (old version) comments
That is a possible way, however this gets very VERY tedious fast. I made a simple game for my virtual computer that required only 8 addresses of ROM (16 bits per address), which was doable, i'm currently planning on making a waay more powerful and advanced computer, so I can run more heavy workloads on it, but i would need multiple hundreds of bytes to make an actual game. At some point I will start using a 16x16 display for running the game, but for now this will do: my project.