Sega Saturn

Hardware

Processors

The Saturn is powered by two Hitachi SH2, 32-bit RISC processors. These particular SH-2 chips run at 28Mhz, and are capable of processing up to 25 million instructions per second (MIPS) each, for a combined rating of 50 MIPS (MIPS however, is not a true indication of processor performance in many cases). Each SH2 comes with an internal 4K RAM

cache in order to speed up processing tasks.

• Two Hitachi SuperH-2 7604 32-bit RISC processors at 28.63 MHz (25 MIPS)—each has 4 kB on-chip cache, of which 2 kB can alternatively be used as directly addressable Scratchpad RAM

• SH-1 32-bit RISC processor (controlling the CD-ROM) (originally this was going to be the only processor until Sega heard of the PlayStation specs)

• Custom VDP 1 32-bit video display processor (running at 7.1590 MHz on NTSC Systems, 6.7116 MHz for PAL Systems)

• Custom VDP 2 32-bit video display processor (running at 7.1590 MHz on NTSC Systems, 6.7116 MHz for PAL Systems)

• Custom System Control Unit (SCU) with DSP for geometry processing and DMA controller (running at 14.3 MHz)

• Motorola 68EC000 sound controller (running at 11.3 MHz / 1.5 MIPS)

• Yamaha FH1 DSP sound processor, "Saturn Custom Sound Processor" (SCSP), running at 22.6 MHz

• Hitachi 4-bit MCU, "System Manager & Peripheral Control" (SMPC)

Memory

The Saturn is equipped with 16 megabits (2 megabytes) of main RAM. 12 megabits of video RAM. And 512K of audio RAM.

• 1 MB SDRAM as work RAM for both SH-2 CPUs (faster)

• 1 MB DRAM as work RAM for both SH-2 CPUs (slower)

• 512K VDP1 SDRAM for 3D graphics (Texture data for polygon/sprites and drawing command lists)

• 2x 256K VDP1 SDRAM for 3D graphics (Two framebuffers for double-buffered polygon/sprite rendering)

• 512K VDP2 SDRAM for 2D graphics (Texture data for the background layers and display lists)

• 4 KB VDP2 SRAM for color palette data and rotation coefficient data (local, on-chip SRAM)

• 512 KB DRAM for sound. (Multiplexed as sound CPU work RAM, SCSP DSP RAM, and SCSP wavetable RAM)

• 512 KB DRAM as work RAM for the CD-ROM subsystem's SH-1 CPU

• 32 KB SRAM with battery back-up for data retention.

• 512 KB Mask ROM for the SH-2 BIOS

Audio

The Saturn Custom Sound Processor (SCSP) is manufactured by Yamaha

and consists of several components.

The SCSP is a multi-function game sound generator LSI that consists

of a PCM sound generator and DAC (Digital Audio Converter). The SCSP

creates processes sound mixes. It contains 32 slot sound generator

and sound effect DSP, 16 channel digital mixer and timer, and an

interrupt controller. The Saturn's audio RAM is connected directly

to the SCSP, and is used to store the sound programs (ie. Cybersound)

or raw waveform samples. The SCSP can support up to 32 channels for

PCM playback, or 8 channels for FM synthesis modulation. Maximum

sample rate for PCM samples is 44.1Khz (CD Quality). The SCSP is

MIDI-compliant, and can be hooked up to external equipment (such

as keyboards).

The 128 step Digital Signal Processor is capable of generating

special effects such as reverberation and different room acoustics.

The entire SCSP is controlled by a single Motorola 68EC000 16-bit

CPU running at 11.3Mhz. The MC68EC000 is essentially the same as

(and compatible with) the M68000 used in the Megadrive and several

other consoles, but without the 8-bit MC6800 interface. The SCSP can

be directly accessed by the MC68EC000 and both SH2s.

The SCSP is a fantastic system limited only by the small amount of

RAM made available to it, and a lack of hardware sample compression.

• 22.6 MHz Yamaha FH1 digital signal processor

• Any of 32 slots can be linked together for multiple operators per FM sound channel

• Usually four operators used per slot for eight FM channels total

• 44.1 kHz sampling rate

Video

Both VDP chips have direct access to the both SH2s, as well asdirect memory access (DMA) to both the main and video RAM.The Sega Saturn is equipped with dual custom VDP chips for graphics processing. The VDP1 chip is primarily responsible for sprite generation. Polygon generation is accomplished through manipulation of the sprite engine. Texture mapping and Gouraud shading is also handled by the VDP1.The VDP1 relies on a dual frame buffer that handles

rotation and stores textures in special 512K cache.

The VDP 2 serves as the Saturn's background processor. Certain special effects such as texture transparency and playfield rotation and scrolling are handled hereThe VDP1 renders primitives to two 256 kB frame buffers that can be configured as 512x512x8 or 512x256x16 (Virtua Fighter 2 was the first game to use high resolution, at 60 frame/s on Consoles). Having two frame buffers allows double buffering of the display and provides more time for rendering. The active framebuffer is read out to the display by the VDP2, which can apply data from a coefficient table to modify the scanning process, for effects like rotation, scaling, and general distortion of the entire frame buffer as a single entity.

The SCU (system bus control unit) provides DMA across a dedicated bus commonly labeled as the "B-bus" that the VDP2 and VDP1 are connected to, allowing transfer of data from them to and from main memory. Keep note that transferring data from and to the same bus is prohibited by all 3 SCU DMA levels.

• Rendering engine for command tables: textured and non-textured polygons, untextured "polygons," "polylines," and lines along with command tables that controls the frame buffer.

• "Sprites" are textured polygons with specific rendering modes:

• Normal sprite (one point), shrunk/scaled sprite (two points), distorted sprite (four points)

• Other rendering modes:

  • Overwrite (replace frame buffer contents)

  • Shadow (underlying frame buffer pixels rewritten with 1/2 brightness, primitive not drawn)

  • Half luminosity (primitive rendered with 1/2 brightness)

  • Half transparency (primitive and underlying framebuffer pixels averaged together)

  • Gouraud shading for RGB-format textures only

  • Dual 256KB frame buffers

  • Programmable frame buffer depth of 8 or 16 bits per pixel

  • Automatic erase feature to clear framebuffer with single color

Some commonly quoted specifications are highly dependent on the rendering modes for the polygons and other factors that burden the system load:

• 200,000 texture-mapped polygons per second

• 500,000 flat-shaded polygons per second

• 60 frames of animation per second

In order to better understand the differences between the PS1 GPU and Saturn VDP1 rendering capabilities, here are some varying factors:

PS1 GPU

• The GPU has a 2 kB texture cache.

• The GPU has a unified 1 MB block of memory for the texture data and frame buffers. This allows for complex effects where the framebuffer is in turn applied as a texture again.

• The framebuffer portion of the GPU RAM must be manually erased.

• Commands are sent to the GPU via DMA, buffered in a FIFO, and executed in the order of being sent.

Saturn VDP1

• The VDP1 has no texture cache.

• VDP1 memory is split: 512 kB for texture data / command lists, 256 kB for one framebuffer and 256 kB for another.

• The two frame buffers have a high-speed auto-erase feature.

• Commands are stored in a linked list in RAM, multiple lists can be stored, the list can be processed by the VDP1 without wasting a DMA channel.

The VDP 2 serves as the Sega Saturn's background processor. Certain special effects such as texture transparency and playfield rotation and scrolling (up to five fields at any given time) are handled here.

Both the VDP2 and VDP1 32-bit video display processor have direct access to the bothSH2s, as well as direct memory access (DMA) to both the main and video RAM.

• Background engine

• Four simultaneous scrolling backgrounds

• Uses 8x8 or 16x16 tiles or bitmap display per background

• Programmable memory access controller for VDP2 VRAM

• Two simultaneous rotating playfields

• VDP2 can rotate VDP1 framebuffer position while scanning out to display for rotation effects

• Color RAM supports 15-bit (32768 colors) and 24-bit (16.7 million colors) display modes

• Programmable priority at the per-background / per-tile / per-pixel levels

• Background color tinting/fading, and transparency effects

• Background blur effect (gradation) to simulate distance

Programmable display resolution:

• Horizontal sizes of 320, 352, 640, 704 pixels

• Vertical sizes of 224, 240, 256 scanlines, non-interlaced

• Vertical sizes of 448, 480, 512 scanlines, interlaced (only PAL consoles support 256 and 512 scanline displays)

• Hi-Vision (EDTV) and 31 kHz (VGA) display support:

• 31 kHz: 320×480 or 640×480, non-interlaced (progressive scan)

• Hi-Vision: 352×480 or 704×480, non-interlaced (progressive scan)

Storage

The Sega Saturn features a double speed CD-ROM drive manufactured by JVC-Victor (some models may have been manufactured by Hitachi or Sanyo). The drive has a transfer rate of 320 KB/s, and a 512 KB data cache. Drive related functions are controlled via a single Hitachi SH1 32-bit RISC processor operating at 20 MHz.

• Audio CD compatible

• CD+G compatible

• CD+EG compatible

• CD single (8 cm CD) compatible

• Video CD (required optional MPEG add-on), Photo CD, Electronic Books, digital karaoke (optional)

Input/output

• Two 7-bit bidirectional parallel I/O ports (controller ports)

• High-speed serial communications port (Both SH2 SCI channels and SCSP MIDI, also used for the Serial port)

• Cartridge connector

• Internal expansion port for optional MPEG adapter card (different models available from Sega, JVC, and Hitachi)

• Composite video/audio (standard)

• NTSC/PAL RF (optional RF adapter required)

• S-Video compatible (optional cable required)

• RGB compatible (optional cable required)

• EDTV/Hi-Vision compatible (custom cable required, not commonly available)

While the Saturn graphics hardware is capable of VGA (progressive/non-interlaced) video, no existing retail software ever used this mode and the system cannot force any such software to run in this mode. Moreover, neither Sega nor third-party manufacturers produced or sold the cables required to support such high-resolution modes on any type of display.

Power source

• AC120 volts; 60 Hz (US)

• AC240 volts; 50 Hz (EU)

• AC100 volts; 60 Hz (JP)

• 3 volt lithium battery to power non-volatile RAM and SMPC internal real-time clock

• Power Consumption: 25 W

• Power Consumption: 12 W (JP)

Dimensions (US/European model)

• Width: 260 mm (10.2 in)

• Length: 230 mm (9.0 in)

• Height: 83 mm (3.2 in)

Errata

VDP1 transparency rendering quirk causes strips of pixels to be rewritten to framebuffer for 2-point (scaled) and 4-point (quadrangle) "sprites", applying the transparency effect multiple times. Rarely seen in commercial games (Robotica explosions), later titles implemented software transparency via direct framebuffer access to correctly render polygons (Dural in Virtua Fighter Kids).

Another technique developed for pseudo-hardware transparency was to rasterize polygons using one or two pixel tall sprites with transparency enabled to fill in horizontal spans. Because 2 of the 4 quadrangle points were identical, there was no framebuffer rewrite during rendering.

The Linux kernel contains code specifically designed for the Saturn; it is unclear if this effort was ever completed.

External Hardware

Supporting additional peripherals

DirectLink

The DirectLink (also known as Link Cable) is a device that enables two Sega Saturns to connect to each other for multiplayer gameplay. The device requires two televisions and two copies of the same game.

Action Replay

The Action Replay can be used to change the code of certain games in order to gain access to features not meant to be accessed or to advance further into a game using cheats. Another feature of the Action Replay was the ability to back-up saved games for when the battery dies. It was also possible to play imported games from any region without any modification to the system.

Arcade Racer

Arcade Racer is a type of joystick designed after a steering wheel for the Sega Saturn. As the controller is an analog control mechanism, it possesses a smoother response and is considered ideal for a variety of Sega Saturn games, such as:

• Time Warner Interactive's V.R. Virtua Racing

• Sega's Daytona USA.

• Sega's Sega Rally Championship

• Sega's Sega Touring Car Championship

Storage Cards

Utilizing the cartridge slot behind the CD tray, portable storage cards are inserted to store game information such as high scores and saved game files. This was one of the few accessories for the Sega Saturn to be available to third-party manufacturers.

Notable Qualities

Unlike the PlayStation and Nintendo 64 which used triangles as its basic geometric primitive, the Saturn rendered quadrilaterals. This proved to be a hindrance because most of the industry's standard design tools were based around triangles. One of the challenges brought forth by quadrilateral-based rendering was problems with making some shapes, notably triangular objects. This can be seen in the Saturn version of Tomb Raider, in which triangular rocks are not rendered as well as other systems' versions of the game. The hardware also lacked light sourcing and hardware video decompression support, the latter being a major disadvantage during a time when full-motion video was quite popular.

Still, if used correctly, the quadrilateral rendering of the Saturn had advantages. It could potentially show less texture distortion than was common with PlayStation titles, as demonstrated by several cross-platform titles such as Wipeout and Destruction Derby. The quadrilateral-focused hardware and a 50% greater amount of video memory also gave the Saturn an advantage for 2D game engines and attracted many developers of RPGs, arcade games and traditional 2D fighting games. With creative programming, later games like Burning Rangers were able to achieve true transparency effects on hardware that used simple polygon stipples as a replacement for transparency effects in the past.