Difference between revisions of "L0 ROM"

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Latest revision as of 23:50, 10 June 2019

Toshiba LO ROM chip taken from an AES system.
LO ROM chip found on a CDM3-2 board.

The L0 ROM is a 64KiB (sometimes 128KiB with A16 tied to ground) ROM chip found in every NeoGeo systems, which contains byte values used by LSPC to shrink sprites vertically.

The dump is called 000-lo.lo in system ROM sets.

Hash

  • CRC32: 5A86CFF2
  • SHA-1: 5992277DEBADEB64D1C1C64B0A92D9293EAF7E4A

Data format

The data is made of 256 tables of 256 bytes, each table corresponding to a vertical shrinking value for sprites.

For the first 256 lines (top half of a full sprite), the index in the table is the line number of the sprite currently being drawn (scanline - Y position).

Each byte entry in the table is used as 2 nibbles:

  • The upper nibble is the tile number index to read in the tilemap in VRAM SCB1 (0 to 15).
  • The lower nibble is the line number of that tile to fetch in the C ROMs.

For the last 256 lines (bottom half of a full sprite), the index in the table is complemented: the table is read backwards.

  • The upper nibble is the tile number index XOR $1F to read in the tilemap in VRAM SCB1 (16 to 31).
  • The lower nibble is the line number XOR $F of that tile to fetch in the C ROMs.

Example of GPU processing

Ngscaling.png

(Maybe place this part in the LSPC page ?)

Sprite with Y zoom value = $1B and tile height = 2 (32 pixels).

Sprite line # L0 address L0 data Tilemap index Tile line used
0 $1B00 $00 0 0
1 $1B01 $08 0 8
2 $1B02 $10 1 0
...
26 $1B1A $E8 14 8
27 $1B1B $F8 15 8
28 $1B1C $FF 15 15
29 $1B1D $FF 15 15
...

Datasheet

Official TC531001 datasheet: [[1]]