Help to find mistake for Circuit with NO SRAM
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1. NO BLATANT PIRACY. This includes reproducing homebrew less than 10 years old, with the exception of free software.
2. No advertising your reproductions, with the exception of free software.
3. Be nice. See RFC 1855 if you aren't sure what this means.
Help to find mistake for Circuit with NO SRAM
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.
My /CART connected to cart edge pin 49
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.
My /CART connected to cart edge pin 49
Re: Help to find mistake for Circuit with NO SRAM
Can you explain what those multiplexors are doing? And what makes you think that the menu could work if the multiplexors don't work?
Re: Help to find mistake for Circuit with NO SRAM
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.
Re: Help to find mistake for Circuit with NO SRAM
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.
Re: Help to find mistake for Circuit with NO SRAM
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 ?
Re: Help to find mistake for Circuit with NO SRAM
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.
Quietust, QMT Productions
P.S. If you don't get this note, let me know and I'll write you another.
P.S. If you don't get this note, let me know and I'll write you another.
Re: Help to find mistake for Circuit with NO SRAM
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.
Quietust, QMT Productions
P.S. If you don't get this note, let me know and I'll write you another.
P.S. If you don't get this note, let me know and I'll write you another.
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Re: Help to find mistake for Circuit with NO SRAM
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.
Re: Help to find mistake for Circuit with NO SRAM
Yes, exactly 332s and 160s.poorstudenthobbyist wrote: ↑Tue Mar 30, 2021 9:38 amYou 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.
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 ?
Re: Help to find mistake for Circuit with NO SRAM
No one can confirm me please
Re: Help to find mistake for Circuit with NO SRAM
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?
Re: Help to find mistake for Circuit with NO SRAM
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?
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?
Re: Help to find mistake for Circuit with NO SRAM
Hi fisher,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?
Thanks you.
I will try to check up , maybe I forgot something.
Re: Help to find mistake for Circuit with NO SRAM
Taking a better look at the schematics, shouldn't you be enabling only one of the multiplexers?
It looks like both are being enabled and having their output connected to the bus at the same time.
Maybe I'm not understanding it totally, but isn't a not gate needed in this case?
It looks like both are being enabled and having their output connected to the bus at the same time.
Maybe I'm not understanding it totally, but isn't a not gate needed in this case?