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Keep original prom + new eprom in cart.. bus contamination?

Posted: Wed Sep 04, 2013 6:56 am
by bytestorm
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.

Re: Keep original prom + new eprom in cart.. bus contaminati

Posted: Wed Sep 04, 2013 9:22 am
by MottZilla
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.

Re: Keep original prom + new eprom in cart.. bus contaminati

Posted: Wed Sep 04, 2013 9:32 am
by bytestorm
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!

Re: Keep original prom + new eprom in cart.. bus contaminati

Posted: Wed Sep 04, 2013 9:56 am
by bazz
/CE

Re: Keep original prom + new eprom in cart.. bus contaminati

Posted: Wed Sep 04, 2013 9:58 am
by bazz
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

Re: Keep original prom + new eprom in cart.. bus contaminati

Posted: Wed Sep 04, 2013 11:34 am
by qwertymodo
Both should work, I'd go with /CE for the sake of power consumption.

Re: Keep original prom + new eprom in cart.. bus contaminati

Posted: Wed Sep 04, 2013 11:47 am
by bytestorm
Nice!! Thanks :)

Re: Keep original prom + new eprom in cart.. bus contaminati

Posted: Wed Sep 04, 2013 11:49 am
by MottZilla
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.

Re: Keep original prom + new eprom in cart.. bus contaminati

Posted: Wed Sep 04, 2013 3:18 pm
by Memblers
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).

Re: Keep original prom + new eprom in cart.. bus contaminati

Posted: Wed Sep 04, 2013 3:18 pm
by qwertymodo
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

Re: Keep original prom + new eprom in cart.. bus contaminati

Posted: Wed Sep 04, 2013 3:46 pm
by bazz
You guys are so helpful. *BRAVO*

Re: Keep original prom + new eprom in cart.. bus contaminati

Posted: Wed Sep 04, 2013 8:33 pm
by bytestorm
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.

Re: Keep original prom + new eprom in cart.. bus contaminati

Posted: Wed Sep 04, 2013 11:37 pm
by Markfrizb
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

Re: Keep original prom + new eprom in cart.. bus contaminati

Posted: Thu Sep 05, 2013 3:16 am
by bytestorm
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!

Re: Keep original prom + new eprom in cart.. bus contaminati

Posted: Thu Sep 05, 2013 9:00 am
by qwertymodo
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.