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I've seen a lot of discrepancy on this topic, and I'd like a final answer.

The old SG-1000 document on this site says 8kb at $a000 and mirrored at $c000, Meka emulates 4kb at $c000 mirrored at $d000 with nothing at $a000-$bfff, Sega Retro says 1kb, and most of the commercial games set the stack pointer either $c3ff or $c400, suggesting only 1kb of RAM is really there.

SC-3000 has most definitely 2KBytes.
SG-1000 and SG-1000 II both have TMM2009 chips which are 1KByte.

I recall years ago, someone made a test ROM to verify that (by doing a simple mirroring test).

OK thanks for the info.

Would it be appreciated if I tried to write a more up-to-date document on the SG-1000? There's not a lot I've found on the internet.

All the useful knowledge has been migrating to the wiki so by all mean feel free to add stuff there.

We should make it even clearer that the Documents page, apart from Charles' docs is pretty much outdated stuff.

I would like to be sure about the WRAM in SG-1000. Is the WRAM TMM2009P-A chip a 1KB or 2KB chip? According to information he is:

TMM2009P-A ("16,384 bits high speed and low power static random access memory organized as 2,048 words by 8 bits and operates from a single 5V supply")

How is it? Is it a 2KB chip but the SG-1000 only uses 1KB, or is it some corrupted 2KB versions running as 1KB?

I also have a question about the VRAM 2KB map in the SG-1000 because the information is unclear.

It is also not clear whether VRAM has 2KB or 16KB? There are 8 pieces of MB8118 memory, but they are single-bit, so 8-bit is 2KB - right? https://sega.jp/fb/segahard/sg1000/data.html

Tilemap is divided into three 32x8 tiles size parts - one part should be 256 bytes, e.g:

- $0000-$00FF
- $0800-$08FF
- $1000-$10FF
- $1800-????? (sprite pattern table?)

Exactly at what address each part of the tilemap begins and ends, and what is the pattern table (I understand there are separate pattern tables for each of the three parts?)

Enri has a schematic: http://www43.tok2.com/home/cmpslv/Sg1000/EnrSG.htm

The pin that would have been A10 is marked by Enri as being an extra +CE, and is tied to +5V. Perhaps earlier models used a 8 kibibit SRAM instead. Or maybe the TMM2009 actually means 8 kibibit.

MAME's source comments:

Quote

TMM2009. This RAM is completely undocumented (even in Toshiba Databooks of the era) but the schematic shows it has a pinout that matches TMM2016/6116 2k x8-bit SRAM

Video DRAM has 7 address pins - 14 address signals - so there's 2^14 = 16384 addresses with memory. Eight chips = 16384 bytes

(To be fair: not all DRAMs use all address bits on both /RAS and /CAS - for example, N's FDS uses 4 DRAMs each with 4-bit data buses, and use 8 and then 6 address lines on the RAS and CAS)

Thanks. I've already read a lot about it and there's 1KB WRAM and 16KB VRAM. But it was uncertain.

What does the exact VRAM map of the SG-1000 look like?

Sprite attribute table: 128 bytes (4 bytes per sprite, 32 sprites)
Sprite tiles: 2048 bytes (256 tiles, 8 bytes per tile)
Background tiles: 6144 bytes (768 tiles, 32×24 tiles, 256×192 pixels, 8 bytes per tile)

$0000-$07FF - Tiles graphics for the top part (2048)
$0800-$0FFF - Tiles graphics for the middle part (2048)
$1000-$17FF - Tiles graphics for the bottom part (2048)
$1800-$1FFF - Used for sprites tiles graphics (2048)
$2000- ?

That's all the information I found.

It can be whatever you want - the TMS9918 provides a lot of configurability. The options depend on what video mode you're using (Text? Graphics 1? 2?)

Mode 1/2: 256x192 resolution, tilemap, 2 colors per tile, 8 bytes per tile

Can Tilemap also be anywhere in VRAM?

Yes.

Author	Message
Karmic Joined: 18 Jan 2017 Posts: 9 Location: Canada	So how much RAM does the SG-1000 have? Posted: Wed Jan 18, 2017 4:32 am
Karmic Joined: 18 Jan 2017 Posts: 9 Location: Canada	I've seen a lot of discrepancy on this topic, and I'd like a final answer. The old SG-1000 document on this site says 8kb at $a000 and mirrored at $c000, Meka emulates 4kb at $c000 mirrored at $d000 with nothing at $a000-$bfff, Sega Retro says 1kb, and most of the commercial games set the stack pointer either $c3ff or $c400, suggesting only 1kb of RAM is really there.

TmEE Joined: 31 Oct 2007 Posts: 853 Location: Estonia, Rapla city	Posted: Wed Jan 18, 2017 7:00 am
	SC-3000 has most definitely 2KBytes. SG-1000 and SG-1000 II both have TMM2009 chips which are 1KByte.

KingMike Joined: 14 Oct 2008 Posts: 510	Posted: Wed Jan 18, 2017 4:56 pm
KingMike Joined: 14 Oct 2008 Posts: 510	I recall years ago, someone made a test ROM to verify that (by doing a simple mirroring test).

Karmic Joined: 18 Jan 2017 Posts: 9 Location: Canada	Posted: Thu Jan 19, 2017 1:05 am
Karmic Joined: 18 Jan 2017 Posts: 9 Location: Canada	OK thanks for the info. Would it be appreciated if I tried to write a more up-to-date document on the SG-1000? There's not a lot I've found on the internet.

Bock Site Admin Joined: 08 Jul 2001 Posts: 8648 Location: Paris, France	Posted: Thu Jan 19, 2017 9:26 am
	All the useful knowledge has been migrating to the wiki so by all mean feel free to add stuff there. We should make it even clearer that the Documents page, apart from Charles' docs is pretty much outdated stuff.

siudym Joined: 23 Sep 2021 Posts: 99 Location: Poland	Posted: Fri Dec 10, 2021 2:21 pm
siudym Joined: 23 Sep 2021 Posts: 99 Location: Poland	I would like to be sure about the WRAM in SG-1000. Is the WRAM TMM2009P-A chip a 1KB or 2KB chip? According to information he is: TMM2009P-A ("16,384 bits high speed and low power static random access memory organized as 2,048 words by 8 bits and operates from a single 5V supply") How is it? Is it a 2KB chip but the SG-1000 only uses 1KB, or is it some corrupted 2KB versions running as 1KB? I also have a question about the VRAM 2KB map in the SG-1000 because the information is unclear. It is also not clear whether VRAM has 2KB or 16KB? There are 8 pieces of MB8118 memory, but they are single-bit, so 8-bit is 2KB - right? https://sega.jp/fb/segahard/sg1000/data.html Tilemap is divided into three 32x8 tiles size parts - one part should be 256 bytes, e.g: - $0000-$00FF - $0800-$08FF - $1000-$10FF - $1800-????? (sprite pattern table?) Exactly at what address each part of the tilemap begins and ends, and what is the pattern table (I understand there are separate pattern tables for each of the three parts?)

lidnariq Joined: 24 Mar 2021 Posts: 120	Posted: Fri Dec 10, 2021 8:01 pm
lidnariq Joined: 24 Mar 2021 Posts: 120	Enri has a schematic: http://www43.tok2.com/home/cmpslv/Sg1000/EnrSG.htm The pin that would have been A10 is marked by Enri as being an extra +CE, and is tied to +5V. Perhaps earlier models used a 8 kibibit SRAM instead. Or maybe the TMM2009 actually means 8 kibibit. MAME's source comments: Quote TMM2009. This RAM is completely undocumented (even in Toshiba Databooks of the era) but the schematic shows it has a pinout that matches TMM2016/6116 2k x8-bit SRAM Video DRAM has 7 address pins - 14 address signals - so there's 2^14 = 16384 addresses with memory. Eight chips = 16384 bytes (To be fair: not all DRAMs use all address bits on both /RAS and /CAS - for example, N's FDS uses 4 DRAMs each with 4-bit data buses, and use 8 and then 6 address lines on the RAS and CAS)

siudym Joined: 23 Sep 2021 Posts: 99 Location: Poland	Posted: Fri Dec 10, 2021 10:17 pm
siudym Joined: 23 Sep 2021 Posts: 99 Location: Poland	Thanks. I've already read a lot about it and there's 1KB WRAM and 16KB VRAM. But it was uncertain. What does the exact VRAM map of the SG-1000 look like? Sprite attribute table: 128 bytes (4 bytes per sprite, 32 sprites) Sprite tiles: 2048 bytes (256 tiles, 8 bytes per tile) Background tiles: 6144 bytes (768 tiles, 32×24 tiles, 256×192 pixels, 8 bytes per tile) $0000-$07FF - Tiles graphics for the top part (2048) $0800-$0FFF - Tiles graphics for the middle part (2048) $1000-$17FF - Tiles graphics for the bottom part (2048) $1800-$1FFF - Used for sprites tiles graphics (2048) $2000- ? That's all the information I found.

lidnariq Joined: 24 Mar 2021 Posts: 120	Posted: Fri Dec 10, 2021 11:03 pm
lidnariq Joined: 24 Mar 2021 Posts: 120	It can be whatever you want - the TMS9918 provides a lot of configurability. The options depend on what video mode you're using (Text? Graphics 1? 2?)

siudym Joined: 23 Sep 2021 Posts: 99 Location: Poland	Posted: Sat Dec 11, 2021 10:45 am
siudym Joined: 23 Sep 2021 Posts: 99 Location: Poland	Mode 1/2: 256x192 resolution, tilemap, 2 colors per tile, 8 bytes per tile Can Tilemap also be anywhere in VRAM?

lidnariq Joined: 24 Mar 2021 Posts: 120	Posted: Sat Dec 11, 2021 7:16 pm
lidnariq Joined: 24 Mar 2021 Posts: 120	Yes.

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