Making a Repro Using Sx-ROM

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Izen6
Posts: 53
Joined: Mon Jan 28, 2019 9:53 pm

Making a Repro Using Sx-ROM

Post by Izen6 » Sun Mar 08, 2020 8:13 am

I'm trying to make a repro of Chip's Challenge for NES for myself and I'm using an SG-ROM donor board as there is only a PRG that is needed. I tried wiring everything up using the following guide:

Using a 27C040
Bend up pins 1, 2, 24, 30, and 31
Connect pin 1 to hole 30
Connect pin 2 to hole 24
Connect pin 24 to pin 16
Connect pin 30 to hole 1
Connect pin 31 to hole 2

The game does start and goes to the title screen, but when I start to play it brings me to a level and the character is not there and nothing happens. I can pause the game and skip levels, but it's like Chip is missing. Any thoughts? Thanks!

Izen6
Posts: 53
Joined: Mon Jan 28, 2019 9:53 pm

Re: Making a Repro Using Sx-ROM

Post by Izen6 » Mon Mar 09, 2020 7:35 am

I'm wondering, would a graphical or character glitch mean that I might need to use an SN-ROM board without battery? Would WRAM in addition help to make a difference?

Ice Man
Posts: 546
Joined: Fri Jul 04, 2014 2:34 pm

Re: Making a Repro Using Sx-ROM

Post by Ice Man » Mon Mar 09, 2020 9:52 am

The ROM is 128KB of PRG ROM, no Battery, no PRG RAM.

Your problem is, that SNROM/SGROM only supports up to 256KB of PRG ROM (27C020).
Wire Pin 31 of your EPROM to VCC or GND and Pin 1 to VCC.

Izen6
Posts: 53
Joined: Mon Jan 28, 2019 9:53 pm

Re: Making a Repro Using Sx-ROM

Post by Izen6 » Mon Mar 09, 2020 12:12 pm

I'll give it a shot! Thanks! So if I had used the 27C020 I shouldn't have had an issue? Jeez, wish I didn't run out of them.

Izen6
Posts: 53
Joined: Mon Jan 28, 2019 9:53 pm

Re: Making a Repro Using Sx-ROM

Post by Izen6 » Mon Mar 09, 2020 12:36 pm

Should I change the wiring I already have or just add more wires for what you recommended? Right now I have pin 30 to hole 1
and pin 31 to hole 2.

Ice Man
Posts: 546
Joined: Fri Jul 04, 2014 2:34 pm

Re: Making a Repro Using Sx-ROM

Post by Ice Man » Mon Mar 09, 2020 1:26 pm

Change the wiring.

27C040 is perfectly fine, but the MMC1 only handles PRG up to 256KB (A17 max) in normal cases.
SUROM allows 512KB but that requires rewiring of the MMC1/PRG RAM as well and isn't needed here as the default PRG was only 128KB.

Th 27C040 has A18 at pin 31 which is not needed and therefore HAS to be connected to either VCC or GND.
Pin 1 (VPP) should always be held high (VCC) as well unless stated otherwise in the datasheet.

For easier understanding:
Pin 1 of 27C040 (VPP) connected to VCC
Pin 2 of 27C040 (A16) connected to hole 24
Pin 24 of 27C040 (/OE) connected to GND
Pin 30 of 27C040 (A17) connected to hole 1
Pin 31 of 27C040 (A18) connected to GND or VCC

Izen6
Posts: 53
Joined: Mon Jan 28, 2019 9:53 pm

Re: Making a Repro Using Sx-ROM

Post by Izen6 » Mon Mar 09, 2020 5:03 pm

When you say Pin 1 to VCC or Pin 24 to GND, you mean to the pins of the chip and not to holes, right? Thanks so much for your help!

Izen6
Posts: 53
Joined: Mon Jan 28, 2019 9:53 pm

Re: Making a Repro Using Sx-ROM

Post by Izen6 » Mon Mar 09, 2020 6:55 pm

Also, do I need to lift different pins? Right now I have pins 1, 2, 24, 30 and 31 lifted.

Ice Man
Posts: 546
Joined: Fri Jul 04, 2014 2:34 pm

Re: Making a Repro Using Sx-ROM

Post by Ice Man » Tue Mar 10, 2020 2:17 am

Just these pins, not any others.
It does not matter where you grab VCC or GND from.

Izen6
Posts: 53
Joined: Mon Jan 28, 2019 9:53 pm

Re: Making a Repro Using Sx-ROM

Post by Izen6 » Tue Mar 10, 2020 5:49 am

Thanks! I'm going to give it a try today. I'll post how it turns out!

Izen6
Posts: 53
Joined: Mon Jan 28, 2019 9:53 pm

Re: Making a Repro Using Sx-ROM

Post by Izen6 » Tue Mar 10, 2020 10:40 am

So I tried rewiring and get the same issue tried pin 31 to pin 32 and then tried it to pin 16. Could it be something with CHR-RAM, or could it be a ROM issue? I think the ROM has a header since it's 129kb and not 128kb. Could that be the issue? My chip wrote and verified.

Ice Man
Posts: 546
Joined: Fri Jul 04, 2014 2:34 pm

Re: Making a Repro Using Sx-ROM

Post by Ice Man » Tue Mar 10, 2020 10:47 am

If you didn't remove the header then there's your problem.
The iNES headers are only needed for emulation. FC/NES carts do not have them.

Use a tool such as famiROM for that.

Izen6
Posts: 53
Joined: Mon Jan 28, 2019 9:53 pm

Re: Making a Repro Using Sx-ROM

Post by Izen6 » Tue Mar 10, 2020 11:01 am

When I split the ROM with Famirom, does it automatically get rid of the header, or do I need to do anything else? The ROM itself is 129kb, but when I split with Famirom I get a 512kb ROM (since I'm using the 27C040).

Ice Man
Posts: 546
Joined: Fri Jul 04, 2014 2:34 pm

Re: Making a Repro Using Sx-ROM

Post by Ice Man » Tue Mar 10, 2020 11:50 am

It removes the header and only outputs PRG and CHR (if present).
If you did that already, post pictures of your soldering/cart.

Izen6
Posts: 53
Joined: Mon Jan 28, 2019 9:53 pm

Re: Making a Repro Using Sx-ROM

Post by Izen6 » Tue Mar 10, 2020 12:31 pm

Attached a picture.
Attachments
IMG_20200310_152945.jpg

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