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HVC-ETROM, possible to modify for 2 x 32KB SRAMs?
https://forums.nesdev.com/viewtopic.php?f=28&t=15179
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Author:  ZeroShift [ Wed Nov 30, 2016 11:25 am ]
Post subject:  HVC-ETROM, possible to modify for 2 x 32KB SRAMs?

I've been doing research on reproduction games lately, no hardware to do it but have been contemplating getting an EPROM flasher. After finding infidelity's Super Mario All-Stars NES and not being able to play it with my N8 I got curious and dug around to see if it was possible to even make this repro.

famiROM and nestopia say it uses 64K of SRAM, 32 for saving and 32 for WRAM but no games in existence use this setup. However, the NESDev wiki says that NES-ETROMs can be modified to support that amount of SRAM with the SL/CL15 solder pads. Of course ETROM games are absurdly expensive, but their FC counterparts are much cheaper. I don't plan on destroying any games anytime soon but I can't find any info on if the HVC-ETROM boards can be modified in the same way.

So is it possible to modify an HVC-ETROM board to support 2 x 32KB SRAM chips? Unless I'm completely blind I can't find SL15 or CL15 on the FC game boards.

Author:  lidnariq [ Wed Nov 30, 2016 11:31 am ]
Post subject:  Re: HVC-ETROM, possible to modify for 2 x 32KB SRAMs?

Nope, the famicom version lacks the trivial solder jumper option.

Reworking HVC-EWROM might be a tiny bit easier, since it only requires adding one wire (PRG RAM 1 /CE) instead of two (PRG RAM A13 and PRG RAM A14)

Author:  ZeroShift [ Wed Nov 30, 2016 11:44 am ]
Post subject:  Re: HVC-ETROM, possible to modify for 2 x 32KB SRAMs?

So using this it's possible to instead modify an HVC-EWROM with 64KB? Sorry, I'm still relatively new to this.

The one wire from PRG RAM 1 /CE to on this board accomplishes a similar effect?

Author:  lidnariq [ Wed Nov 30, 2016 11:58 am ]
Post subject:  Re: HVC-ETROM, possible to modify for 2 x 32KB SRAMs?

So, EWROM comes with one 32 KiB RAM.
It's connected to the following relevant signals from the MMC5: PRG RAM 0 /CE, PRG RAM A13, PRG RAM A14, PRG RAM /WE, and PRG RAM Vcc, while the other 23 pins are just connected to pins on the cartridge connector.

ETROM and EKROM, instead, come with two or one 8 KiB RAMs. They're instead connected to PRG RAM 0 /CE, PRG RAM 1 /CE on ETROM, PRG RAM +CE, PRG RAM /WE, and PRG RAM Vcc. Pin 1 on HVC-ETROM is tied to PRG RAM Vcc, while on NES-ETROM it's tied to PRG RAM A14.

To get a 64 KiB layout, you need PRG RAM 0 /CE and PRG RAM 1 /CE, one for each RAM, and PRG RAM A13 and PRG RAM A14 to address 32 KiB in each RAM.

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