what does he mean with "open bus"???PPUADDR (0x2006):
This is the register where you write the address that you want to
read from or write to using PPUDATA (0x2007). Games must not ever
write to this address during rendering, or it will mess up the display,
this will be explained in a later section. Reading here will return
open bus. During rendering the address written here will be the
"program counter" for the PPU, so this is why it messes up, because
the PPU also increments that register as its rendering leading to
addresses you don't want. Only use this during vblank to update
graphic data.
a little noob question: ¿open bus?
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a little noob question: ¿open bus?
extracted from "The software emulation of the NES concole" (a.k.a. "Qeed's Doc"):
Open Bus means that no device responds to the address requested. So the value returned is generally the last value placed onto the bus. You don't need to worry about this so early on in your project. Infact you may never really need to worry about accurate open bus behavior. The only games that might rely on this are probably obscure chinese pirates.
