Multi cart SRAM question. Need some help

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Mbumstead
Posts: 19
Joined: Wed Aug 21, 2013 5:00 pm

Multi cart SRAM question. Need some help

Post by Mbumstead » Tue Oct 03, 2017 1:29 pm

Hello everyone. I'm building a 4 in 1 multicart right now. I know how to hijack the top two address pins of the prom and run it through a 74ls161 to switch between roms with the reset button. What I'm having trouble with is doing the same thing with the sram. I think I've assumed incorrectly thinking I could do the same thing by hijacking the rop two address pins. But that's not working for me. If anyone could give me some advice here I would great,y appreciate it.


I'm trying to use a 256k sram chip and split it into 4 , 64k banks.


And thank you in advance for your help.

lidnariq
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Location: Seattle

Re: Multi cart SRAM question. Need some help

Post by lidnariq » Tue Oct 03, 2017 1:43 pm

Your assumption is basically correct. It's more likely some other mistake.

tepples
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Re: Multi cart SRAM question. Need some help

Post by tepples » Tue Oct 03, 2017 3:52 pm

If the games don't use a battery, you don't need to bank the SRAM.

What mapper are we dealing with? MMC1, MMC3, or something else? Four battery-backed banks on an MMC1 might be tricky because it generates only +CE, requiring an inverter to turn it into /CE for the 256 kbit SRAM. The SXROM board has such an inverter.

Mbumstead
Posts: 19
Joined: Wed Aug 21, 2013 5:00 pm

Re: Multi cart SRAM question. Need some help

Post by Mbumstead » Tue Oct 03, 2017 4:32 pm

I'm working with mmc1. Battery backed sram. So , I'm correct in assuming that I can hijack the top two address pins just like the eprom?

lidnariq
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Location: Seattle

Re: Multi cart SRAM question. Need some help

Post by lidnariq » Tue Oct 03, 2017 4:33 pm

Yup.

When the 74'161 loses power, its output will fall to ground, but all the other address lines will also when the Nintendo is turned off. So that shouldn't be relevant.

Mbumstead
Posts: 19
Joined: Wed Aug 21, 2013 5:00 pm

Re: Multi cart SRAM question. Need some help

Post by Mbumstead » Thu Oct 05, 2017 10:24 am

Thank you. I’ll build it tonight. I appreciate the advice.

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