Help to find mistake for Circuit with NO SRAM

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Kayumba
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Help to find mistake for Circuit with NO SRAM

Post by Kayumba » Thu Mar 25, 2021 9:17 am

Hello to all.
I tried to do one circuit for carts 16/32Mbit without SRAM.
But could not find my mistake.
Game menu starts but after some selections it's seam to be like a corrupted.
I tested the same EPROM on other boards, its works fine.
Dont understand what happened ...
Should be something wrong with Multiplexers ?
Can you help me please.
Image
My /CART connected to cart edge pin 49
Image

nocash
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Re: Help to find mistake for Circuit with NO SRAM

Post by nocash » Thu Mar 25, 2021 8:57 pm

Can you explain what those multiplexors are doing? And what makes you think that the menu could work if the multiplexors don't work?
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Kayumba
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Re: Help to find mistake for Circuit with NO SRAM

Post by Kayumba » Fri Mar 26, 2021 2:09 am

nocash wrote:
Thu Mar 25, 2021 8:57 pm
Can you explain what those multiplexors are doing? And what makes you think that the menu could work if the multiplexors don't work?
Maps the data from EPROM (16-bit bus) to the SNES cartridge (8-bit bus).

what makes me think...
I don’t know what to think,
I checked all Lo/HiRom connexions , all seams to be right.
Multiplexers too, but problem is here.

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Fisher
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Re: Help to find mistake for Circuit with NO SRAM

Post by Fisher » Fri Mar 26, 2021 9:16 am

A good way to at least start troubleshooting is to try to read the ROM on the circuit, as it was the console reading it and compare the data you got with what you should be getting.

Kayumba
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Re: Help to find mistake for Circuit with NO SRAM

Post by Kayumba » Mon Mar 29, 2021 9:47 am

Fisher wrote:
Fri Mar 26, 2021 9:16 am
A good way to at least start troubleshooting is to try to read the ROM on the circuit, as it was the console reading it and compare the data you got with what you should be getting.
I still looking for my mistakes.
I think my mistake should be on some wrong connections between /CE , /RD , and /CART

Just to be sure,
Board (Game) without saves only need "Multiplexers" chip, am I right?
74HC139 chip are only to use with SRAM chip on board, is it right ?

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Quietust
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Re: Help to find mistake for Circuit with NO SRAM

Post by Quietust » Mon Mar 29, 2021 10:01 am

If your circuit works in the "menu" but not in-game, I would suspect that maybe the chips aren't fast enough - it's possible that the menu only runs at 1.79MHz but the games might try to run at 2.68MHz or 3.58MHz.
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Re: Help to find mistake for Circuit with NO SRAM

Post by Kayumba » Mon Mar 29, 2021 11:05 am

Quietust wrote:
Mon Mar 29, 2021 10:01 am
If your circuit works in the "menu" but not in-game, I would suspect that maybe the chips aren't fast enough - it's possible that the menu only runs at 1.79MHz but the games might try to run at 2.68MHz or 3.58MHz.
OK, and how to correct it ?

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Re: Help to find mistake for Circuit with NO SRAM

Post by Quietust » Mon Mar 29, 2021 11:32 am

Kayumba wrote:
Mon Mar 29, 2021 11:05 am
Quietust wrote:
Mon Mar 29, 2021 10:01 am
If your circuit works in the "menu" but not in-game, I would suspect that maybe the chips aren't fast enough - it's possible that the menu only runs at 1.79MHz but the games might try to run at 2.68MHz or 3.58MHz.
OK, and how to correct it ?
I was only suggesting a possible explanation for the problem - I'm not an electronics expert, so I have no idea how to actually fix it.

To figure out if it's really a timing problem, get the datasheets for the exact chips you used and look at their response times (specifically enable/disable times, transition times, and propagation delays). If they're too high, then find faster versions of the chips - 1.79MHz ought to be able to handle 280ns, 2.68MHz should handle 210ns, and 3.58MHz would need at least 140ns or lower.

Edit: in addition to the multiplexers, you should also make sure that the EPROM itself is capable of handling those higher speeds.
Last edited by Quietust on Tue Mar 30, 2021 9:59 am, edited 1 time in total.
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Re: Help to find mistake for Circuit with NO SRAM

Post by poorstudenthobbyist » Tue Mar 30, 2021 9:38 am

Kayumba wrote:
Mon Mar 29, 2021 9:47 am
Just to be sure,
Board (Game) without saves only need "Multiplexers" chip, am I right?
74HC139 chip are only to use with SRAM chip on board, is it right ?
You can make a board run on nothing but an EPROM, or you could add 10 unnecessary decoders, and it could still work. It all depends on how you're wiring the board, what chips you're using, what you're trying to accomplish, and how robust you make the design.

For a board with no SRAM you don't need a decoder to switch between ROM and RAM, because you'll never be accessing RAM. You might need multiplexers, it depends on the EPROMs you're using. I'm assuming you're using 332s or 160s, in which case you will probably need multiplexers.
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Re: Help to find mistake for Circuit with NO SRAM

Post by Kayumba » Tue Mar 30, 2021 10:32 am

poorstudenthobbyist wrote:
Tue Mar 30, 2021 9:38 am
Kayumba wrote:
Mon Mar 29, 2021 9:47 am
Just to be sure,
Board (Game) without saves only need "Multiplexers" chip, am I right?
74HC139 chip are only to use with SRAM chip on board, is it right ?
You can make a board run on nothing but an EPROM, or you could add 10 unnecessary decoders, and it could still work. It all depends on how you're wiring the board, what chips you're using, what you're trying to accomplish, and how robust you make the design.

For a board with no SRAM you don't need a decoder to switch between ROM and RAM, because you'll never be accessing RAM. You might need multiplexers, it depends on the EPROMs you're using. I'm assuming you're using 332s or 160s, in which case you will probably need multiplexers.
Yes, exactly 332s and 160s.
Thank you :)

Like I supposed,
I made some tests with suspected connections between CARTRIDGE EDGE and EPROM for /CE , /RD , and /CART.

Here is my actual, most be wrong connections witch do bug my games WITHOUT SAVES and of course NO SRAM on board:

CARTRIDGE EDGE pin 23 "/RD" => EPROM pin 11 "CE"
CARTRIDGE EDGE pin 49 "/CART" => Multiplexers 74HC257D pin 15 "OE"
EPROM pin 13 "OE" => GND


Here the way how I connected and make it works :

CARTRIDGE EDGE pin 23 "/RD" => EPROM pin 13 "OE"
CARTRIDGE EDGE pin 49 "/CART" => Multiplexers 74HC257D pin 15 "OE"
CARTRIDGE EDGE pin 49 "/CART" => EPROM pin 11 "CE"
EPROM pin 13 "OE" => GND


I have seen somewhere that somebody had the same problem (dont remember where),
so I just note it on the paper...and test it later.
Impossible to find again where I got this information.
Can somebody clarify me please, what do I done ?
Why it should be connected like that ?

As it explained here by my "Sensei" :
https://thepoorstudenthobbyist.com/2019 ... planation/
"/CART and /RD come from the SNES, so these signals represent what the SNES wants from the cartridge"
And he says that :
" the /CART signal should drive the /CE pin"
exactly what I done :
CARTRIDGE EDGE pin 49 "/CART" => EPROM pin 11 "CE"
"and the /RD signal should drive the /OE pin"
exactly what I done :
CARTRIDGE EDGE pin 23 "/RD" => EPROM pin 13 "OE"


Sensei says about Bus Conflicts of multiplexers and propose solution to do like that :
My solution has always been to use /CART to drive the ROM /OE signal, and then reroute the ROM’s /OE signal to the multiplexers...
Its what I done :
CARTRIDGE EDGE pin 49 "/CART" => Multiplexers 74HC257D pin 15 "OE"

Not sure if I get right and if I should also connect it to EPROM pin 13 "OE" ?

and ground the ROM’s /OE.
what I done :
EPROM pin 13 "OE" => GND

Except mentioned on red color connection, all work's like that.
Can you confirm me please if its right connections for games WITHOUT SRAM ?

Kayumba
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Re: Help to find mistake for Circuit with NO SRAM

Post by Kayumba » Wed Apr 07, 2021 2:14 pm

:( No one can confirm me please :( :( :(

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Re: Help to find mistake for Circuit with NO SRAM

Post by nocash » Wed Apr 07, 2021 3:20 pm

You are telling us that you have wired /RD to GND and that it does make it works. What kind of comments are you hoping for?
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Fisher
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Re: Help to find mistake for Circuit with NO SRAM

Post by Fisher » Sun Apr 11, 2021 6:47 pm

The only time I saw something similar was when a guy suggested cutting one of the ROM pins to make it work fine with a SNES' Game Genie.
In the end, I figured out that a small resistor mod would do the job better and not cause any kind of damage to the cartridges.
Maybe the circuit just needs a pull-up or pull-down resistor?

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Re: Help to find mistake for Circuit with NO SRAM

Post by Kayumba » Mon Apr 12, 2021 1:01 pm

Fisher wrote:
Sun Apr 11, 2021 6:47 pm
The only time I saw something similar was when a guy suggested cutting one of the ROM pins to make it work fine with a SNES' Game Genie.
In the end, I figured out that a small resistor mod would do the job better and not cause any kind of damage to the cartridges.
Maybe the circuit just needs a pull-up or pull-down resistor?
Hi fisher,
Thanks you.
I will try to check up , maybe I forgot something.

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