Help with Legend Of Zelda repro

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lidnariq
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Re: Help with Legend Of Zelda repro

Post by lidnariq » Sun Mar 06, 2016 2:39 pm

How expensive are random electronic components to you? I might be able to figure out something to implement the mirroring control using programmable logic (GAL20V8, 22V10, or maybe random 74xx parts), but whether that's worthwhile depends on what you have easy and affordable access to.

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Fisher
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Re: Help with Legend Of Zelda repro

Post by Fisher » Sun Mar 06, 2016 3:23 pm

It depends of the parts.
Most stuff I have made are from parts I got from old peripherals or even junk.
Most parts are expensive here, since where I live is essentially a rural area.
The PAL chips need to be programmed, right? How hard is to do it?
I ask because for writting the flash ROMs I use an old PC motherboard.
Could this be used to write the PAL chips?
Maybe the best way would be with random 74xx logic.
If you help me, I'll be very happy!
I just took a look at the docs and can't even imagine how that stuff could be implemented!
Thanks in advance!

lidnariq
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Re: Help with Legend Of Zelda repro

Post by lidnariq » Sun Mar 06, 2016 4:54 pm

Fisher wrote:The PAL chips need to be programmed, right? How hard is to do it?
It's not too hard, but you would probably need to build special hardware for it, e.g. http://www.etc.tuiasi.ro/cin/Downloads/ ... atics.html
I ask because for writting the flash ROMs I use an old PC motherboard.
Could this be used to write the PAL chips?
Probably not; most flash ROMs only require a single voltage to program, but GALs always required multiple.
Maybe the best way would be with random 74xx logic.
Uh, well, try this, I guess:
mmc1-mirroring-control.png
mmc1-mirroring-control.png (2.19 KiB) Viewed 5320 times

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Fisher
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Re: Help with Legend Of Zelda repro

Post by Fisher » Mon Mar 07, 2016 3:52 am

Chip hunting season!! :lol:
As soon as I have some results I'll post here, as usual.
Many thanks for now!!

@Tepples:
Sorry. I've read the manual, but I just could not diferentiate traces from dots. :roll:
Looks like I need to train my ears at least to know who is who.
Anyways, I would like thank you, for this awesome program!!

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Re: Help with Legend Of Zelda repro

Post by lidnariq » Mon Mar 07, 2016 12:32 pm

As far as availability goes, there's a lot of available substitutions.

You can replace the 4002/74'4002 with a 74'138, 74'139, 74'23, or 74'25.
You can replace the the 74'164 with a 74'96, 74'198, 74'199, 74'299, &c
You can replace the 74'153 with a 74'253, 74'151, 74'153, &c.

I don't know whether mixing technologies from radically different eras (e.g. 74F with 74ACT) will work.

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Fisher
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Re: Help with Legend Of Zelda repro

Post by Fisher » Fri Mar 11, 2016 6:02 pm

Well, I just can't get the 74'164 or similar.
Seems to not be much used on old PC motherboards.
I thought in trying to make something similar witn an 74'374 or maybe 2x 74'175, but the complexity of the circuit would be greater.
I'll try to order from Aliexpress... let's see if I can get the things before 3 months...

Anyway, looks like I've found another MMC3 clone.
I'll open another thread to discuss this.
Thanks for now. I'll try to build this as soon as I get all components.

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Re: Help with Legend Of Zelda repro

Post by lidnariq » Fri Mar 11, 2016 6:19 pm

I think we could probably get away with using an ordinary D-register (e.g. three 74'74, a 74'176, a 74'374, &c) as long as we have at least five bits of storage.

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Fisher
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Re: Help with Legend Of Zelda repro

Post by Fisher » Fri Apr 08, 2016 9:34 am

I'm worried about putting too many ICs on this.
First, because I'm doing a "spider" kind of assembly, second because I'm not sure of how many ICs can be powered safely on a NES cartridge?
I already have the ROM, 2SRAMs, the MMC1's clone, the decoding and protection circuit.
It's 6 ICs!!
If I add 6 more: 4x 74'74, a 74'138 and a 74'153 I'll have a very nice rat's nest and a cartridge that may consume too much power.
I've ried an 74'374 without success, it may be deffective... I just plugged the outputs on the inputs, plugging the last output on the first input. Is this idea correct?
Can somehing like this be made with an 74'373? I think Ican get one of these from an old NES that should be working...

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Re: Help with Legend Of Zelda repro

Post by lidnariq » Fri Apr 08, 2016 10:32 am

Fisher wrote:I'm not sure of how many ICs can be powered safely on a NES cartridge?
Depends on the specific technology of the 74xxx parts you're using. 74HC or 74AC you should be able to use a whole bunch. Plain no-letter variants, not so many.

Note that GALs are already much more thirsty than discrete logic, and some boards use multiple GALs or many many 74xx ICs, so I think this particular issue is unlikely to come up.

The standard front-loading US NES has a 1A 5V power supply, and uses 350mA of that for the CPU/PPU/&c. Obviously whatever you're using could vary...
I've tried an 74'374 without success, it may be deffective... I just plugged the outputs on the inputs, plugging the last output on the first input. Is this idea correct?
Uh, maybe? Plugging 2D into 1Q, 3D into 2Q, &c, to make a shift register? That should work.
Can somehing like this be made with an 74'373? I think Ican get one of these from an old NES that should be working...
No; the '373 is a transparent latch; when its +LATCH signal is high the value will just shoot right through all eight bits. This really needs registers with their clock input.

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Fisher
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Re: Help with Legend Of Zelda repro

Post by Fisher » Fri Apr 15, 2016 8:48 am

WOW!! That's quite a lot of random logic!! :o
I finally could draw the schematics of what I intend to do.
I'm trying Eagle, if you know a better/easier software that's Linux frienly please let me know.

Could this possibly work?
mmc mirror.png
Looks like a little messed up.
I'm not sure who would be the A output, so I'm throwing a little guess...
I really like Lidnariq's design, it's a lot cleaner!!
Any chance I could get some free sample ICs from any manufacturer?

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Re: Help with Legend Of Zelda repro

Post by lidnariq » Fri Apr 15, 2016 11:14 am

'374 should always be enabled.
CPU D0 should go to '374 1D.

You don't care about faked shift register after the two bits that go into the multiplexer. Since it's a register, you could even safely leave 6D..8D floating (but you should probably tie them to ground or +5V)

Otherwise looks right.
---

I keep on trying to like KiCAD, but I keep on finding it unusable. GEDA is ... better, but I still like Eagle more. Xfig and Xcircuit are ancient passable solution for schematics, but don't do layout at all. LTSpice (via wine) won't do layout, but does let you simulate things.


You're extremely unlikely to get free samples of any legacy part (like 74xx). You might be able to scavenge a GAL for free, though... but you'll have to find/borrow a programmer.

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Fisher
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Re: Help with Legend Of Zelda repro

Post by Fisher » Thu Jul 28, 2016 8:11 am

Back on this old topic again!!
Made the corrections as you told.
I'm having trouble drawing the PCB, it don't show the Vcc connection on the ICs.
What am I missing?
New schematics.
New schematics.

lidnariq
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Re: Help with Legend Of Zelda repro

Post by lidnariq » Thu Jul 28, 2016 10:10 am

Don't tie the '374 outputs to ground: leave them floating.

This looks like Eagle? If so, the 74xx ICs should have an implicit connection to "Vcc" and "Gnd" nets, and their power pins should already be connected to each other.

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Fisher
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Re: Help with Legend Of Zelda repro

Post by Fisher » Tue Sep 06, 2016 6:10 pm

Sorry for the long delay, but this project is driving me nuts!!
I've built the circuit over 10 times and I always find to have one or two defective parts!! :cry:
Is there a way to know if a game uses this kind of mirroring switching before trying it on the real hardware?
I've tried Megaman 2 and some graphics appear glitched on the intro :-(
I think this may be the same cause.
The idea of buying a cheap JRPG to do this mod is starting to appear good...
Anyway, thanks for the support, you're great!!

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Re: Help with Legend Of Zelda repro

Post by tepples » Tue Sep 06, 2016 6:48 pm

You can assume that anything using SGROM uses mirroring switching, as it's the only significant difference in overall capability compared to UNROM or BN/AOROM.

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