Help with Legend Of Zelda repro

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Fisher
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Location: -29.794229 -55.795374

Re: Help with Legend Of Zelda repro

Post by Fisher » Wed Sep 07, 2016 2:00 pm

Yes I did. But unfortunatelly I end up discovering this bugged MMC1 :-(
I think there may be some games that don't use this feature.
I have a Chip'n Dale (1) working fine on a board very similar to this (with MMC1 implemented as an epoxy blob). I'm not sure if the games aren't hacked, but this board had Goal 2, the other was Stealth ATF, and if I remember well, I've seem Ninja Gaiden (1), Double Dragon (1) and Predator, all sold and manufactured by the same trademark: Gradiente/Falcom Soft.
I don't know if would be possible to figure it out with a debugger, or taking a look on the game's PRG data.
Looks like it's a matter of put sockets on this board and see what will work fine or not.

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Fisher
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Re: Help with Legend Of Zelda repro

Post by Fisher » Thu Oct 06, 2016 5:48 pm

Well... As I have read in aother post, quitters don't learn!!
Looks like the '138 wiring is wrong here...
According to this truth table, I would have 7 other conditions that would drive any of the outputs high.
I think the clock needs the transition from low to high.
I can't see how I could do this with an '138 without a inverter.
Can this be done?

lidnariq
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Re: Help with Legend Of Zelda repro

Post by lidnariq » Thu Oct 06, 2016 6:16 pm

The '374 latches its contents on a rising edge.

The '138 generates a low pulse on one /Y0 through /Y7 for the duration of all the six inputs matching. So, yes, it generates a falling edge when /ROMSEL falls, and a rising edge when /ROMSEL rises, and yes, that means it's a tiny bit delayed relative to the CPU's data bus ... BUT that shouldn't be a problem. The CPU's data bus should remain floating until after the value from the data bus is safely latched inside the '374.

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Fisher
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Re: Help with Legend Of Zelda repro

Post by Fisher » Thu Oct 06, 2016 6:38 pm

So... again I'll start over...
I thought in give up of this board, but no! I'm learning a lot while trying to fix this :-)
I think I should make a PCB for this thing, it would make troubleshoot easier.

The "spider" just confuses me more each time I need to check something.
I always need a multmeter to confirm what is soldered where.
Just a really big rat's nest :-(

lidnariq
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Re: Help with Legend Of Zelda repro

Post by lidnariq » Thu Oct 06, 2016 6:40 pm

Try adding resistors and LEDs to the '374s outputs so you can see if it's actually working?

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Fisher
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Re: Help with Legend Of Zelda repro

Post by Fisher » Mon Nov 28, 2016 4:36 pm

Finally!!
I could get a 100% working solution for my Zelda repro!!
Zelda BR - Frente
Zelda BR - Frente
Zelda BR - Solda
Zelda BR - Solda
Zelda BR - Montado
Zelda BR - Montado
Unfortunatelly I had to kill a Famicom original, that's something I'm not very proud of :cry:
It was Nobunaga No Yabou, and, as far as I could know, this was a kind of boring action RPG, just like Royal Blood, that I'm planning to do a Castlevania 3 repro on it. Anyway I'm saving the original maskroms, just in case I need to undo these mods in the future... who knows what the furure reserves!!
I took in account many opinions posted here, mostly the Bregalad's ones, wich I agree most of the time.

Although the other board has a bugged (or should I say cut-down) version of the MMC1, I now know some games that work fine with this setup. This include Stealth ATF, Chip 'n Dale, Goal! and even the buggy Bionic Commando ROM I've flashed.
Surprisingly, the Bionic Commando takes a lot more time to crash in that board.
Any suggestion about some trick I could use to debug it?
The game don't seems to crash on emulators, even Nestopia, wich I think is one of the most accurate emulators around.

Many thanks guys!!
I've learned a lot of things while trying to make these repros.
In special, from you Lidnariq and Tepples you guys really rocks!!
Both you and many others around have a huge knowledge and are nice enough to share!!
Again, many thanks guys!!

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