Open bus test results?

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Zepper
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Open bus test results?

Post by Zepper »

Here's the output result of 3 emulators (latest version).
I'm targetting the joypads (Controllers 1 and 2).
Which one is correct?
joy_test.png
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Zepper
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Re: Open bus test results?

Post by Zepper »

OK.
I don't get the APU open bus $40 $40 $3f, but $40 $40 $40.
What is the pulse 2 read ?
lidnariq
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Re: Open bus test results?

Post by lidnariq »

Literally quoting the first link I included,
tepples wrote: Thu Mar 26, 2015 2:02 pm "APU open bus" is the result of reading $4006 and $4007. The first two should be $40. The third [rides] the open bus from $3F06 to $4006
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Zepper
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Re: Open bus test results?

Post by Zepper »

lidnariq wrote: Fri Apr 16, 2021 2:20 pm Literally quoting the first link I included,
tepples wrote: Thu Mar 26, 2015 2:02 pm "APU open bus" is the result of reading $4006 and $4007. The first two should be $40. The third [rides] the open bus from $3F06 to $4006
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).
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Re: Open bus test results?

Post by tepples »

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.
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