Basically you reset all buttons to 0 and set the ones which you want to be 0 you separately activate to make them 1 - or vice versa.
That allows a single button and a single and to store 1 bit of information.
Reading is done by resetting everything and look which buttons give a different output. After a read you need to refresh the storage.
other TODOs:
I will update the 4x4 bit ram with a 8x8 version (in 2z), but I think I have to increase the size for a bank from 9x9x2 to 9x10x2 or use a double "9x9x4" because the logic is more advanced and I don't wanna spend more than 10% on controll-blocks
It will also require a special 9x9x2 or even 9x10x2 controller because it should redo the value automatically to be useful for beginners.
It will also have the connections on top where possible thus you can build a computer room and walk through the banks to see which bits are set / repair damage without walking through cables.
I will post more details when I upload the final version.