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After purchasing a SC-3000 Basic III A repro PCB from EBay, I wanted to see if expanded RAM support could be added to a library I'm working on.

Looking through MAME, it's pretty easy to trick MAME into thinking a SG-1000 cartridge contains extra RAM.
The Dahjee cartridges are enabled by setting the ROM size to 49152 and filling the space between $2000 and $3FFF with $FF.

The Castle is probably the easiest method. At location $1CC3, you include the string "ASCII 1986". And the cartridge has to be 32k.

Once I had my cartridge running through MAME and MEKA, I burned it to a 32k EPROM, and it worked.

When run on a cartridge with SRAM, it will show a RAM icon in the upper right. Right now, all I do is move the stack to the end of RAM, and set a flag.

Edit:
Here's the board I used.
https://www.pcbway.com/project/shareproject/SC_3000_Sega_Basic_Level_IIIA_e54cd768.html

Test.zip (1.75 KB)

This makes it sound like MAME has some brittle ROM detection techniques instead of properly configuring the memory map based on the identity of the ROM, which is a bit surprising. Having arbitrary ASCII at a certain address seems like an odd way to manage it. A ROM hash could be used for the set of known dumps, and homebrew presumably would need to offer some metadata to opt in to certain behaviour - although I don’t know of any standard for this.

Maxim wrote

This makes it sound like MAME has some brittle ROM detection techniques instead of properly configuring the memory map based on the identity of the ROM, which is a bit surprising.

It does. I've had my rom detected as a Codemasters rom and an X-Terminator rom. Both break MAME, since it can't determine a "slot".

cdoty wrote

After purchasing a SC-3000 Basic III A repro PCB from EBay, I wanted to see if expanded RAM support could be added to a library I'm working on.

Looking through MAME, it's pretty easy to trick MAME into thinking a SG-1000 cartridge contains extra RAM.
The Dahjee cartridges are enabled by setting the ROM size to 49152 and filling the space between $2000 and $3FFF with $FF.

The Castle is probably the easiest method. At location $1CC3, you include the string "ASCII 1986". And the cartridge has to be 32k.

Once I had my cartridge running through MAME and MEKA, I burned it to a 32k EPROM, and it worked.

When run on a cartridge with SRAM, it will show a RAM icon in the upper right. Right now, all I do is move the stack to the end of RAM, and set a flag.

Edit:
Here's the board I used.
https://www.pcbway.com/project/shareproject/SC_3000_Sega_Basic_Level_IIIA_e54cd768.html

Hi! The cartridge PCB you linked from pcbway is the same you bought from ebay?

Author	Message
cdoty Joined: 29 Jun 1999 Posts: 68 Location: Houston TX	SG-1000/SC-3000 expanded RAM. Posted: Tue Oct 17, 2023 10:38 am Last edited by cdoty on Tue Oct 17, 2023 6:03 pm; edited 1 time in total
cdoty Joined: 29 Jun 1999 Posts: 68 Location: Houston TX	After purchasing a SC-3000 Basic III A repro PCB from EBay, I wanted to see if expanded RAM support could be added to a library I'm working on. Looking through MAME, it's pretty easy to trick MAME into thinking a SG-1000 cartridge contains extra RAM. The Dahjee cartridges are enabled by setting the ROM size to 49152 and filling the space between $2000 and $3FFF with $FF. The Castle is probably the easiest method. At location $1CC3, you include the string "ASCII 1986". And the cartridge has to be 32k. Once I had my cartridge running through MAME and MEKA, I burned it to a 32k EPROM, and it worked. When run on a cartridge with SRAM, it will show a RAM icon in the upper right. Right now, all I do is move the stack to the end of RAM, and set a flag. Edit: Here's the board I used. https://www.pcbway.com/project/shareproject/SC_3000_Sega_Basic_Level_IIIA_e54cd768.html Test.zip (1.75 KB)

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14745 Location: London	Posted: Tue Oct 17, 2023 12:51 pm
	This makes it sound like MAME has some brittle ROM detection techniques instead of properly configuring the memory map based on the identity of the ROM, which is a bit surprising. Having arbitrary ASCII at a certain address seems like an odd way to manage it. A ROM hash could be used for the set of known dumps, and homebrew presumably would need to offer some metadata to opt in to certain behaviour - although I don’t know of any standard for this.

cdoty Joined: 29 Jun 1999 Posts: 68 Location: Houston TX	Posted: Tue Oct 17, 2023 5:56 pm
cdoty Joined: 29 Jun 1999 Posts: 68 Location: Houston TX	Maxim wrote This makes it sound like MAME has some brittle ROM detection techniques instead of properly configuring the memory map based on the identity of the ROM, which is a bit surprising. It does. I've had my rom detected as a Codemasters rom and an X-Terminator rom. Both break MAME, since it can't determine a "slot".

siriokds Joined: 10 Dec 2009 Posts: 115	Posted: Tue Nov 07, 2023 11:13 am
siriokds Joined: 10 Dec 2009 Posts: 115	cdoty wrote After purchasing a SC-3000 Basic III A repro PCB from EBay, I wanted to see if expanded RAM support could be added to a library I'm working on. Looking through MAME, it's pretty easy to trick MAME into thinking a SG-1000 cartridge contains extra RAM. The Dahjee cartridges are enabled by setting the ROM size to 49152 and filling the space between $2000 and $3FFF with $FF. The Castle is probably the easiest method. At location $1CC3, you include the string "ASCII 1986". And the cartridge has to be 32k. Once I had my cartridge running through MAME and MEKA, I burned it to a 32k EPROM, and it worked. When run on a cartridge with SRAM, it will show a RAM icon in the upper right. Right now, all I do is move the stack to the end of RAM, and set a flag. Edit: Here's the board I used. https://www.pcbway.com/project/shareproject/SC_3000_Sega_Basic_Level_IIIA_e54cd768.html Hi! The cartridge PCB you linked from pcbway is the same you bought from ebay?

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