L0 ROM: Difference between revisions

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[[File:cd2_lo.jpg|right|thumb|LO ROM chip found on a CDM3-2 board.]]
[[File:cd2_lo.jpg|right|thumb|LO ROM chip found on a CDM3-2 board.]]


LO stands for "LOokup". It's a 64kB ROM chip found in every NeoGeo systems, which contains byte values used by the GPU to shrink sprites vertically.
The L0 ROM is a 64KiB (sometimes 128KiB with A16 tied to ground) ROM chip found in every NeoGeo systems as a stand alone chip or integrated in another [[NEO-GRZ|chip]], which contains byte values used by {{Chipname|LSPC}} to shrink [[sprites]] '''vertically'''.


The dump is often called 000-lo.lo in [[BIOSes|BIOS]] sets.
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 ROM]]s.
 
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==
[[File:Ngscaling.png|right|thumb]]
 
(Maybe place this part in the LSPC page ?)
 
Sprite with Y zoom value = $1B and tile height = 2 (32 pixels).
 
{|class=wikitable
!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
|-
|colspan=5|...
|-
|26||$1B1A||$E8||14||8
|-
|27||$1B1B||$F8||15||8
|-
|28||$1B1C||$FF||15||15
|-
|29||$1B1D||$FF||15||15
|-
|colspan=5|...
|}
 
==Datasheet==
There are 2 stand alone chip versions used depending on the NeoGeo system, the SOP32 TC531001 and the DIP28 TC531000.
 
Official TC531001 datasheet: [[http://www.alldatasheet.com/datasheet-pdf/pdf/115078/TOSHIBA/TC531001.html]]
 
Official TC531000 datasheet: [[https://www.digchip.com/datasheets/parts/datasheet/710/TC531000CP-pdf.php]]


[[Category:Chips]]
[[Category:Chips]]

Latest revision as of 21:37, 21 May 2020

Toshiba LO ROM chip taken from an AES system.
File:Cd2 lo.jpg
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 as a stand alone chip or integrated in another chip, 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

(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

There are 2 stand alone chip versions used depending on the NeoGeo system, the SOP32 TC531001 and the DIP28 TC531000.

Official TC531001 datasheet: [[1]]

Official TC531000 datasheet: [[2]]