I'm learning about circuitry from the Apple I Replica Creation book. On pp 191-192, it says:
"IRQ - This line is not used by the Apple I."
"RDY - This line is not used by the Apple I."
"NMI - This line is not used by the Apple I."
Later on page 192, it says:
"RDY, /IRQ, and /NMI are tied to High with current-limiting resistors."
My question is: What is this point of this? Why not just leave them disconnected? And even if we do want to keep these lines High, what purpose do the resistors serve?
This is mostly out of curiosity, but also, I'm interested in building the Replica I on a breadboard, since I think that will be more educational than just soldering the chips onto the printed circuit board. And my breadboard is pretty small, so anything I can leave disconnected is helpful.