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PostPosted: Sat Aug 15, 2015 2:06 pm 
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Posts: 304
Joe wrote:
These pictures are helpful, but the chips cover too much to trace the IRQ circuit.

If you remove the chips and take a picture of the empty board, I could trace it. Of course, then you won't be able to play the cartridge anymore (unless you're skilled enough at soldering to take it apart and put it back together).

Do you have anything you could use to trace it? I use a multimeter, but someone else might be able to suggest some other tool if you don't have one of those.



I want to discuss this with the owner of a cassette
I'm just trying to find all kinds of perfect MAPPPER cassette


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PostPosted: Sat Aug 15, 2015 2:19 pm 
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Location: Seattle
There are traces connected to pin 6 (Q6) and pin 10 (↓CP) of the GD4020, so whatever it's counting, it's counting 64 of them. I'd guess it's counting on PPU A12 again, but who knows.


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PostPosted: Sun Aug 16, 2015 12:17 am 
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lidnariq wrote:
There are traces connected to pin 6 (Q6) and pin 10 (↓CP) of the GD4020, so whatever it's counting, it's counting 64 of them. I'd guess it's counting on PPU A12 again, but who knows.




yes,fceux,nestopia src. A12,but not right


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PostPosted: Sun Aug 16, 2015 1:10 am 
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Hm. Not PPU A12. Assuming that the 40-pin IC is a VRC2 clone (and what I can tell looks right), it's clocked by M2. And it appears to feed into the 74'161, so it looks like it's a program-controllable multiple of 64 M2 cycles.


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PostPosted: Wed Aug 19, 2015 1:34 am 
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Joined: Mon Dec 12, 2011 8:15 pm
Posts: 304
Joe wrote:
These pictures are helpful, but the chips cover too much to trace the IRQ circuit.

If you remove the chips and take a picture of the empty board, I could trace it. Of course, then you won't be able to play the cartridge anymore (unless you're skilled enough at soldering to take it apart and put it back together).

Do you have anything you could use to trace it? I use a multimeter, but someone else might be able to suggest some other tool if you don't have one of those.



Is there any progress?


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PostPosted: Wed Aug 19, 2015 3:35 am 
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No. I need to know how the chips are connected to tell you how they work.

Can you trace the connections? Or, can you remove the chips and take a picture of the board with no chips?


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PostPosted: Wed Aug 19, 2015 10:06 am 
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Joined: Sun Apr 13, 2008 11:12 am
Posts: 6273
Location: Seattle
The best I can possibly tell you from just glare-y pictures of the populated PCBs:

1- I believe the 40-pin IC is a VRC2 clone
2- IRQs are clocked by M2
3- IRQs seem to have a divide-by-64 prescaler
4- IRQs seem to be programmable, not fixed.

For us to be able to tell you anything more, you'll either have to get us a picture of the PCBs without the ICs; or sit down with a continuity meter and determine how all the signals are connected.


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