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Keep original prom + new eprom in cart.. bus contamination?
http://forums.nesdev.com/viewtopic.php?f=12&t=10459
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Author:  bytestorm [ Wed Sep 04, 2013 6:56 am ]
Post subject:  Keep original prom + new eprom in cart.. bus contamination?

Hi!
I bought some cheap JAP snes carts that I want to use on my PAL snes.
My plan is to use the translated releases, or american release for some games and put them in the jap cart (same game)

My question is, can i keep the original prom in its place, and just cut /OE or /CE or something and put a switch there, so I can , if wanted, switch it back to the original, JAP version of the game.

I am fully aware that its probably easier to just remove the old chip and put the eprom in its place, BUT I am interested in trying to get this to work, so my question is simply if its possible to shutdown the original chip, and make sure that its not contaminating the bus.

My example cart is Zelda 3 JAP, that i want to put the US release into, and a switch in between.

Best regards.

Author:  MottZilla [ Wed Sep 04, 2013 9:22 am ]
Post subject:  Re: Keep original prom + new eprom in cart.. bus contaminati

Others have done this. You have the right idea. By connecting the ROM control signal through a switch you could switch between two ROM chips. But you shouldn't leave either chip's control line floating.

Whether you use /OE or /CE, the idea is that both ROM's have that signal to a switch that in one position connects ROM A's signal to the board normally, and in the other connects ROM B, all while giving the unconnected ROM +5v to it's signal so that it remains inactive.

Anyway, that's the idea, and people have done it before.

Author:  bytestorm [ Wed Sep 04, 2013 9:32 am ]
Post subject:  Re: Keep original prom + new eprom in cart.. bus contaminati

MottZilla wrote:
Others have done this. You have the right idea. By connecting the ROM control signal through a switch you could switch between two ROM chips. But you shouldn't leave either chip's control line floating.

Whether you use /OE or /CE, the idea is that both ROM's have that signal to a switch that in one position connects ROM A's signal to the board normally, and in the other connects ROM B, all while giving the unconnected ROM +5v to it's signal so that it remains inactive.

Anyway, that's the idea, and people have done it before.


Great!! Thanks :)
I did some searching before posting but couldn't find anything :/
Wich of /OE & /CE is recommended to use? Or is it really no difference?
Thanks for the info so far!

Author:  bazz [ Wed Sep 04, 2013 9:56 am ]
Post subject:  Re: Keep original prom + new eprom in cart.. bus contaminati

/CE

Author:  bazz [ Wed Sep 04, 2013 9:58 am ]
Post subject:  Re: Keep original prom + new eprom in cart.. bus contaminati

the difference is that /CE enables a chip,
/OE enables output of the chip, however output only occurs if /CE is also low.

So it's a matter of disabling the whole chip, vs. keeping both enabled while disabling one's output.

I'd go for just enabling 1 chip at a time, so I voted /CE

Author:  qwertymodo [ Wed Sep 04, 2013 11:34 am ]
Post subject:  Re: Keep original prom + new eprom in cart.. bus contaminati

Both should work, I'd go with /CE for the sake of power consumption.

Author:  bytestorm [ Wed Sep 04, 2013 11:47 am ]
Post subject:  Re: Keep original prom + new eprom in cart.. bus contaminati

Nice!! Thanks :)

Author:  MottZilla [ Wed Sep 04, 2013 11:49 am ]
Post subject:  Re: Keep original prom + new eprom in cart.. bus contaminati

Yes, /CE is probably the way to go. So you'd want a switch ideally that connects one ROM's /CE normally while giving the opposite ROM /CE +5V.

Author:  Memblers [ Wed Sep 04, 2013 3:18 pm ]
Post subject:  Re: Keep original prom + new eprom in cart.. bus contaminati

If you want to use a SPDT switch, you could use a pull-up resistor on each /CE. That's something like a 10K Ohm resistor connected to +5V. That way the /CE won't be disconnected (floating).

Author:  qwertymodo [ Wed Sep 04, 2013 3:18 pm ]
Post subject:  Re: Keep original prom + new eprom in cart.. bus contaminati

Memblers wrote:
If you want to use a SPDT switch, you could use a pull-up resistor on each /CE. That's something like a 10K resistor connected to +5V. That way the /CE won't be disconnected (floating).


I was just about to suggest this, but you beat me to it because I was busy drawing a picture :P

Image

Author:  bazz [ Wed Sep 04, 2013 3:46 pm ]
Post subject:  Re: Keep original prom + new eprom in cart.. bus contaminati

You guys are so helpful. *BRAVO*

Author:  bytestorm [ Wed Sep 04, 2013 8:33 pm ]
Post subject:  Re: Keep original prom + new eprom in cart.. bus contaminati

Yeah you really are :) i am so glad and thanksful for the help!
Every time I post on these forums I get such awesome help and tips.. Really noob friendly place :)
Thanks everyone for helping! I will get the stuff done asap :) just need to get a suitable switch.

Author:  Markfrizb [ Wed Sep 04, 2013 11:37 pm ]
Post subject:  Re: Keep original prom + new eprom in cart.. bus contaminati

A really good and very small Spdt switch is this one...
http://www.mouser.com/Search/ProductDet ... 2-MHSS1105
Right angle too so its very low profile will fit in small places
And .67c

Author:  bytestorm [ Thu Sep 05, 2013 3:16 am ]
Post subject:  Re: Keep original prom + new eprom in cart.. bus contaminati

Markfrizb wrote:
A really good and very small Spdt switch is this one...
http://www.mouser.com/Search/ProductDet ... 2-MHSS1105
Right angle too so its very low profile will fit in small places
And .67c


Only problem for me is the order fee of 20€ just because I am overseas :(
+ shipping around another 20€ at minimum so it's not possible I am afraid. :(
To bad, because mouser have lots of nice things :)

Will have a look around here in Sweden .

But thanks for the tip!

Author:  qwertymodo [ Thu Sep 05, 2013 9:00 am ]
Post subject:  Re: Keep original prom + new eprom in cart.. bus contaminati

Try Digi-Key, AVNet, or Arrow. I'm in the US, so I don't know how their international sales work, but hopefully at least one of them should work for you.

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