This version has some significant changes. I rearranged some variables so six bytes' worth of temp variables are now overlayed with kernel temp variables. Hopefully I've eliminated all conflicts there.
It's now necessary to click twice to remove blocks. This allows for a limited preview/undo function. If you click somewhere and don't want to remove the blocks that turned brown, click somewhere else instead.
I added some feeble sound effects as well. Let me know how they are.
Also, if the machine misses the necessary retrace timing, an error screen will appear. Please write down the numbers or symbols that appear and let me know. Then press fire to return to the game.