I've read on the NesDev Wiki that 2A03 pin 30 is used as a test pin, and that it puts additional registers on $4018-$401A. Does anybody have info about that?
Somewhere here, in "Tech zone", have to be some of my posts about pin 30. Exactly function is unknown(TEST or /SNDEN), probably depends on revision(i've got rev. A CPU, so will check), but CPU's acting different, when pin 30 is"active".
lidnariq wrote:
http://wiki.nesdev.com/w/index.php/Talk:CPU_pin_out_and_signal_description
http://wiki.nesdev.com/w/index.php/User:Quietusthttp://wiki.nesdev.com/w/index.php/File:Apu_address.jpgIt is, admittedly, not unified. But it is all in the wiki.
I didn't find anything when I searched for "pin", "4018" or "tst pin", so I tought there was no info on it.
Anyway, there is no info about what those registers are for. I would try to find out myself by looking at the die photos, but I'm a total n00b at this.
What do you mean when you say "what the registers are for"? The exact function — at least in revision G dies — is described in the last link I posted. And they surely added it for a way to programmatically self-test all the hardware inside the CPUs without needing an ADC.
Oh sorry, I didn't look on the image comments, the mobile phone where I were looking at the picture ran out of memory just after the image was loaded and stopped loading the page