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PostPosted: Tue Apr 24, 2018 4:13 pm 
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Hi.
After discovering that using resistor networks to do level convertion can be reasonably safe and not wanting to "kidnap" that thread, I'm writting this to ask for advice on this.
Since I have a couple of games with 3v memories (and (un)fortunatelly am receiving some more as a gift), I think this can be an easier and quicker mod I could do on these games to make them safer.

What resistor values are fine?
Should they be pull up/down or the data will pass across them?
Thanks in advance.


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PostPosted: Tue Apr 24, 2018 6:09 pm 
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You should be able to get by with voltage dividers on the address & control lines since they're unidirectional. I don't really have a suggestion on bidirectional data lines though. Series resistors will limit the current which is better than unlimited, but the ideal value will depend on drive strength of the console and cart.

You may want to come up with a game genie type device that actually includes proper level shifters, or play on a clone console that runs close to 3v to get around the issue.

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PostPosted: Fri May 04, 2018 4:08 am 
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I've heard that using an HC part like an 74HC244 can make the conversion.
Is it true?


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PostPosted: Fri May 04, 2018 6:53 am 
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LVC


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PostPosted: Fri May 04, 2018 9:01 am 
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Fisher wrote:
I've heard that using an HC part like an 74HC244 can make the conversion.
Is it true?

All the info you need to determine this is spelled out in the datasheet if you know what you're looking for.

Standard HC family devices are not 5v tolerant when supplied by 3.3v. If you look at the Vi (input pin max voltage) it's likely Vcc or Vcc+0.5v. So if you supply Vcc with 3.3v, you'll be exceeding the max input voltage if you apply 5v.

LVC families are generally good for level shifting but are slightly less versatile gate because they can't be supplied by 5v. They will have a Vcc range typically of 1.6-3.6v and Vi max spec of 5.5v. So these can be supplied by 3.3v and have 5v signals applied to their inputs. Their outputs will be relative to the Vcc supply voltage, looking at Vo max it's likely Vcc. So supplied with 3.3v the output pins will be Vcc or less, so you can safely use their outputs to drive 3.3v flash/logic/etc.

AHC is a pretty convenient series because it can be supplied by 3-5v, and is 5v tolerant when supplied by 3v. Vcc is allowed between 2-5.5v, and Vi max is 5.5v. Where HC max Vi is depended on Vcc, AHC Vi max is independent of Vcc. Personally I really like to use these gates because I only have to buy one part in bulk and can utilize it in various designs. It can be supplied by 5v (unlike LVC) so I can use them for a design that's entirely 5v like NES UNROM mapper perhaps. But they can also be used as level shifters when supplied with 3.3v, the Vi max is still 5.5v. Not all devices are offered in AHC series though, but my most commonly used 4x OR gate is availabe with 74AHC32.

There are other families which are good for level shifting, but it comes down to what options are available for your desired logic function.

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PostPosted: Sat May 05, 2018 1:45 am 
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Wouldn't be my first choice, but you probably could use certain 74HC parts, always check the datasheet for the specific chip in question. This quote is from NXP's datasheet for their 74HC245:
Code:
Inputs include clamp diodes. This enables the use of current limiting resistors to interface inputs to voltages in excess of VCC


But it's usually going to be easier to just use LVC, AHC, VHC, LCX, LVT, etc.

As an aside about LVC, when you look into Picogate parts like LVC1G, 2G, etc. you'll find ones that can be powered at 5V. I'm using one like that in my controller port USB peripheral, but I selected one for its partial power-down support.


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PostPosted: Mon Jul 30, 2018 9:02 am 
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The quest for the level convertion continues!!
Maybe it's better to keep my mouth shut than trying to tell guys like these (in portuguese) that this can damage consoles and have already damaged mine. :oops:
That's it... living and learning... hope I'm on the right side!


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PostPosted: Tue Jul 31, 2018 3:42 am 
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Interestingly the guy claims to have the SNES datasheet, and that it states clearly that all components are totally 3.3v tolerant.
I asked him a link to see it by myself!!

Edit: As I tought, the guy says it's available on the Internet and that he can't post a link to it on YT.
The guy also states that Kevtris don't use it, but after I have seem some recent pictures of Kevtris products, it seems that he is using it on the newer versions.
Unless the converters are being used just to shut annoying guys like me :|, I think there's somethig related to it's necessity.


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PostPosted: Tue Jul 31, 2018 4:42 am 
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Fisher wrote:
Interestingly the guy claims to have the SNES datasheet, and that it states clearly that all components are totally 3.3v tolerant.
I asked him a link to see it by myself!!

Edit: As I tought, the guy says it's available on the Internet and that he can't post a link to it on YT.
The guy also states that Kevtris don't use it, but after I have seem some recent pictures of Kevtris products, it seems that he is using it on the newer versions.
Unless the converters are being used just to shut annoying guys like me :|, I think there's somethig related to it's necessity.


I think he's "full of it". Maybe he's saying that the Snes can accept 3 volt data pulses from the cart but there is NO way he can justify the overvoltage of the rom from the console. An original Snes is a 5 volt system after all.
Interestingly, the Chinese say similar things.....i.e. "We use these roms for years and no problems", etc... which means nothing.


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PostPosted: Tue Jul 31, 2018 4:52 am 
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And...
My post was deleted!
Probably I annoyed him too much. :oops:
But AFAIK, I was politely questioning his methods.
Maybe it was because I stated that my SNES was diagnosed on the US by an official technician and I was willing to question it too if I had the datasheet.
Anyone make mistakes, we're humans afterall!!

So, anyone is free to do whatever wants with his properties.
But I think it's nice to tell people what can possibly harm the stuff, so they can choose.
I sincerelly hope that in 20 years or so a 100% working retro console don't become a rarity.
Looks like it's time to keep my mouth shut about this subject...
I think I already know what I need about this and unless the named datasheet surfaces, there's nothing new on the table. :roll:

Edit: Not sure what happened, but my posts are back there.
Since I did similar posts 3 times, I'll delete 2.
Maybe I had a cache problem.


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PostPosted: Tue Jul 31, 2018 6:45 am 
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I could figure out the "datasheet" used as reference:
Attachment:
19732210_1223199171140442_4714194938019949955_n.jpg
19732210_1223199171140442_4714194938019949955_n.jpg [ 18.16 KiB | Viewed 302 times ]

Markfrizb wrote:
Maybe he's saying that the Snes can accept 3 volt data pulses from the cart but there is NO way he can justify the overvoltage of the rom from the console.

I asked for the complete one just to be sure, but it seems exactly as Markfrizb stated.


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PostPosted: Tue Jul 31, 2018 7:46 am 
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Fisher wrote:
I could figure out the "datasheet" used as reference:
Attachment:
19732210_1223199171140442_4714194938019949955_n.jpg

Markfrizb wrote:
Maybe he's saying that the Snes can accept 3 volt data pulses from the cart but there is NO way he can justify the overvoltage of the rom from the console.

I asked for the complete one just to be sure, but it seems exactly as Markfrizb stated.



This is NOT the data sheet for the ROM they are using. I *believe* they are lying based on this:

The part they are using, I surmise, is a S29GL032.
They intentionally blacked out the part number
it's a 48 pin device.
Pin2 of their rom goes to pin5 of their adapter. The S29GL032 rom in BYTE mode would make this pin A15 ~ same as the SNES pin it mates to.
The use of the 2 diodes suggest a 5v ---> 3v conversion.

It can't be the 5v version of the AM29F032D (which is a 48pin device) because that part, pin2 of that rom is not connected internally.

There are NO KNOWN 3v roms that are 5v tolerant, and definitely don't conform to the 5v data sheet he sent to you. I think you can safely say it's a lie/deception.


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PostPosted: Tue Jul 31, 2018 8:22 am 
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Markfrizb wrote:
We use these roms for years and no problems", etc... which means nothing.

They're claiming exactly this!
Also, the guy while trying do do a better explanation said this (translated):

"The processors of the SNES are made to work at TTL tension levels, like:
Low logic level from 0v to 1.8v
High logic level from 1,8 to 5v"
"The bootleg cartridges from the 90's and even Everdrives, Super UFO use 3.3volt memories.
Just do a research about the used material and you'll find that your SNES wasn't damaged because of this problem."

If I understood correctly, he's assuming the pulse tolerance as the continuous current tolerance on the buses again, as stated by Markfrizb before. :roll:
In sum, they're insisting that's level shifters are not necessary.
Also there's a post where they use the Z80 DC Characteristics as a justification, totally ignoring that a console is also made of chipsets that may have different characteristics...


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PostPosted: Tue Jul 31, 2018 9:10 am 
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Fisher wrote:
Markfrizb wrote:
We use these roms for years and no problems", etc... which means nothing.

They're claiming exactly this!
Also, the guy while trying do do a better explanation said this (translated):

"The processors of the SNES are made to work at TTL tension levels, like:
Low logic level from 0v to 1.8v
High logic level from 1,8 to 5v"
"The bootleg cartridges from the 90's and even Everdrives, Super UFO use 3.3volt memories.
Just do a research about the used material and you'll find that your SNES wasn't damaged because of this problem."

If I understood correctly, he's assuming the pulse tolerance as the continuous current tolerance on the buses again, as stated by Markfrizb before. :roll:
In sum, they're insisting that's level shifters are not necessary.
Also there's a post where they use the Z80 DC Characteristics as a justification, totally ignoring that a console is also made of chipsets that may have different characteristics...


Maybe he just doesn't understand the difference?? Yes, the SNES is TTL and can operate under those voltage levels (mostly but not recommended) -- He's probably saying that the SNES will accept the 3.3v signals from the rom as-is......but this isn't where the problem is. He is saying that the data signals don't need to UPCONVERTED and that's kind-of true..... (but doesn't explain the fraudulent data sheet he sent)
So he is not recognizing? the issue of every pin on the 3v rom being fed 5v.

here's ideally what should be done when dealing with 3v rom....
down translate all the address and control lines
power it at 3.3/3.6v
and since the datalines are bidirectional, they should have a transceiver (up and down translates depending on directional flow). --OR-- at a minimum, one way buffer's or something similar so when the snes writes to the sram, the ROM's datalines are not being fed 5v (because they are on the same buss)

I've been dealing with some 3v adapters and this is what I have been dealing with.... to do it "right"
https://youtu.be/JZFaMWE8MRM

The Chinese aren't even using 3v regulators on some of their carts now (I have seen), maybe that's justification (to him) that he doesn't need to use a VR either.... :?


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PostPosted: Tue Jul 31, 2018 11:11 am 
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Being purely a hobbyist, I've been wondering myself about resistors versus level shifters. The consensus seems to be that a level shifter is the right way to do it, and using resistors is more or less "better than nothing" but not ideal. Normally, I would just accept that level shifters are the correct method and that's that. The only reason I question if using resistors is acceptable is because of the popularity of the Everdrive. The Everdrives have a decent user base. Surely, if using resistors was so bad it would be a more widely discussed topic. As in, not just limited to tech circles but even the average person would have some inkling of poor design. But this article on the matter makes a good point, “Well, my device has been working properly for 2 years now." This is like saying, “I’ve been smoking for 2 years and I don’t have cancer. Therefore, smoking does not cause cancer.”


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