Here's the output result of 3 emulators (latest version).
I'm targetting the joypads (Controllers 1 and 2).
Which one is correct?
Open bus test results?
Moderator: Moderators
Re: Open bus test results?
OK.
I don't get the APU open bus $40 $40 $3f, but $40 $40 $40.
What is the pulse 2 read ?
I don't get the APU open bus $40 $40 $3f, but $40 $40 $40.
What is the pulse 2 read ?
Zepper
RockNES author
RockNES author
Re: Open bus test results?
The result should be $40 $40 $3F.
I don't get $3F but $40, since the last address was $4006 (returns high byte of the address).
Zepper
RockNES author
RockNES author
Re: Open bus test results?
If the instruction was an indexed read from $3Fxx, then the last thing on the data bus was the PPU. Reading a write-only register, in this case $3F16 (a mirror of $2006), connects the PPU I/O data bus to the CPU data bus. The PPU I/O data bus holds the last value read from or written to a PPU register.