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Sega Mega-CD/Technical specifications

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Back to: Sega Mega-CD.

Technical specifications for the Sega Mega-CD.

The following are upgrades over the Sega Mega Drive technical specifications.

See Sega Mega Drive technical specifications for details of the base Mega Drive hardware

CPU

  • Main CPU: Motorola 68000 16-bit processor running at 12.5 MHz
  • Same as the Mega Drive. Acts as a co-processor along with the Mega Drive CPU.
  • Bus width: 16-bit
  • Instruction set: 16-bit and 32-bit instructions, 16 registers
  • Performance: 2.19 MIPS
  • Co-processor: Motorola 68000 (Mega Drive CPU) running at 7.67 MHz
  • Bus width: 16-bit
  • Performance: 1.34225 MIPS

Graphics

  • Bus width: 32-bit (2x 16-bit)
  • Bus clock rate: 6.25 MHz (25 MB/s bandwidth)
  • Number of simultaneous colors on screen: 64 (default)
  • Using programming tricks, this limit is increased to 128–256 colors via raster effects.
  • 128–256 colors can be displayed on screen using HAM techniques[2]
  • Planes: 5 layers
  • Sega CD FMV layer
  • 3 enhanced Mega Drive layers (sprite layer, 2 tile layers)
  • Mega Drive back screen
  • Full motion video: Video size from 1/4 to full screen, advanced compression scheme, software-based upgrade
  • On-screen colors available in Cinepak and TruVideo modes: 128–256 colors
  • Sprites/Tilemaps: The Mega-CD features enhancement effects such as scaling and rotation, similar to Sega's Super Scaler arcade hardware and that of the "Mode 7" effect employed by the Super NES. While Mode 7 only supports the scaling and rotation of tilemap backgrounds, the Sega CD supports the scaling and rotation of both the sprites and the tilemap backgrounds.[3]
  • DMA transfer rates: 3.467179 MB/s (VRAM), 6.934358 MB/s (CRAM/VSRAM)
  • Transfer rates during active display: 1.625 MB/s (VRAM), 3.25 MB/s (CRAM/VSRAM)
  • Read/Write fillrate: 6.934358 MPixels/s
  • Write fillrate during active display: 3.25 MPixels/s
  • 3D polygon graphics:[4]
  • Vertex transformations: 16,000 vertices/sec[n 1]
  • Polygon transformations: 5000 triangles/sec,[n 2] 4000 quads/sec[n 3]
  • Framebuffer rendering: 256×160, double-buffered, 15–30 FPS[n 4]
  • Flat shading: 3300 polygons/sec (32-pixel triangles),[n 5] 2100 polygons/sec (64-pixel quads)[n 6]
  • Texture mapping: 2000 polygons/sec[n 7]

Audio

The Mega-CD adds 10 sound channels to the 10 provided by the Mega Drive's sound chips.

  • CD Digital Audio
  • 2-channel stereo
  • 44.1 kHz sampling rate
  • 16-bit PCM audio depth
  • Sound format: 8-bit sign/magnitude monaural PCM (with "stereo" support by allowing each channel to have different volumes on both left and right channels)
  • Maximum sample rate: 32 kHz
  • PCM audio depth: 16-bit[3]
  • Bus width: 8-bit

Other specifications:

  • 16-bit DAC
  • 8x internal over-sampling digital filter
  • Frequency Range: 20 Hz - 20 KHz
  • Signal-to-Noise Ratio: > 90 dB @ 1K
  • Channel Separation: > 90 dB
  • Input: Mixer cable for Mega Drive Model 1 compatibility.
  • Output: Stereo RCA connectors.

Memory

  • Main RAM: 4 Mbit (512 KB)
  • VRAM: 2 Mbit (256 KB)
  • PCM audio samples: 512 Kbit (64 KB)
  • CD-ROM data cache: 128 Kbit (16 KB)
  • Internal Backup RAM: 64 Kbit (8 KB)
  • Main RAM: 25 MB/sec (16-bit, 12.5 MHz, FPM DRAM)[6]
  • VRAM: 25 MB/sec (32-bit, 6.25 MHz, PSRAM)[7]
  • Audio RAM: 12.5 MB/sec (8-bit, 12.5 MHz, SRAM)[8]

Storage

  • 500 MB CD-ROM discs (equivalent to 62 min of audio data)
  • Access time: 800 ms
  • 1/4 screen B/W footage video: 1.5 to 4 hours
  • 1/4 screen color footage: 45 minutes
  • CD-ROM drive transfer rate: 150 Kbytes/s (1x)

(Above specs prior to compression)

Boot ROM

  • Size: 1 Mb (128 KB)
  • Used for games, CD player, CD+G viewing, karaoke (limited to Japanese systems) and regional lockout
  • Region codes: "NA" = North America (NTSC), "EU" = Europe (PAL)
Boot ROM Revisions
Boot ROM Version Machine Download CRC32
0.98 Pioneer LaserActive 0.98 (NA) (info) (88 kB) 8c3e3945
0.98 (Asia) (info) (87 kB) 9f5771d2
1.00 Sega/Mega CD Model 1
Victor WonderMega 1 (Asia)
Sega WonderMega (Asia)
1.00g (Asia, NTSC) (info) (80 kB) 3beb1ac2
1.00l (Asia, NTSC) (info) (84 kB) f18dde5b
1.00o (Asia, NTSC) (info) (80 kB) 1d9756a3
1.00p (Asia, NTSC) (info) (85 kB) 9d2da8f2
1.00s (Asia, NTSC) (info) (84 kB) 79f85384
1.00s (Asia, PAL) (info) (85 kB) 550f30bb
1.00w (Sega WonderMega Bios) (info) (84 kB) d21fe71d
1.00 (NA) (info) (90 kB) e7e3afe2
1.00 (EU) (info) (88 kB) 529ac15a
1.04 Pioneer LaserActive 1.04 (NA) (info) (88 kB) 2ed602d7
1.05 Pioneer LaserActive 1.05 (Asia) (info) (81 kB) b24b919d
1.10 Sega CD Model 1 (minor update) 1.10 (NA) (info) (92 kB) c6d10268
1.11 Mega CD Model 2 (Japan sample/prototype) 1.11 (JP) (info) (86 kB) 4be18ff6
2.00 Sega/Mega CD 2
Victor WonderMega 2 (Asia)
JVC X'Eye (NA)
2.00 (1st NA version) (info) (92 kB) 8af65f58
2.00w (2nd NA version) (info) (92 kB) 9f6f6276
2.00c (Asian version) (info) (85 kB) dd6cc972
2.00 (1st EU version) (info) (90 kB) 0507b590
2.00w (2nd EU version) (info) (90 kB) 4d5cb8da
2.00 (X'Eye) (info) (86 kB) 290f8e33
2.00 (Wondermega) (info) (173 kB) 2b19972f1
2.11 Sega/Mega CD 2, Aiwa CSD G1M (Japan) 2.11w (NA) (info) (93 kB) 2e49d72c
2.11c (JP) (info) (86 kB) 12154531
2.21 Sega Multimega (Europe & Japan), CDX (North America), Linguaphone Education Gear (Japan) 2.21x (MultiMega, EU) (info) (91 kB) aacb851e
2.21x (CDX) (info) (92 kB) d48c44b5

1 The ZIP file contains two dumps, a "good" dump and a "bad" dump. The "bad" dump has an incorrect HINT vector, but is otherwise identical to the "good" dump. The CRC32 listed here is for the "good" dump.

Other

  • Dimensions: 301 mm (11.85") x 212.5 mm (8.366") x 112.5 mm (4.429")
  • Mass: 1.4 kg (3lb 1.384oz)

Notes

  1. 767 cycles per vertex
  2. 2301 cycles per triangle polygon
  3. 3068 cycles per quad polygon
  4. 40 KB memory, 614.4 KB/s (15 FPS) to 1.2288 MB/s (30 FPS) bandwidth, 2.383275 CPU cycles per byte VRAM DMA transfer, 1.464285 MHz (15 FPS) to 2.928568 MHz (30 FPS) DMA, 9.571432 MHz (30 FPS) to 11.035715 MHz (15 FPS) remaining for polygons
  5. 32-pixel polygons, 15 FPS, scanline rendering, 250 cycles/scanline per poly, 3301 cycles/poly (4 scanlines)
    • Polygon memory: 40 bytes per polygon, 8.594 KB memory (220 polygons per frame), 132 KB/s bandwidth (3300 polygons/sec)
  6. 64-pixel polygons, 15 FPS, 250 cycles/scanline per poly, 5068 cycles/poly (8 scanlines)
  7. ASIC's sprite/texture scaling and rotation capabilities can be used for texture mapping rasterization
    • CPU cycles: 2 ASIC command cycles per texel, 128 ASIC command cycles per 8×8 texel texture, 77 cycles DMA transfer (32 bytes) per 8×8 texel texture, 5273 cycles (205 texture cycles) per 8×8 texel polygon
    • Polygon/Texture memory: 72 bytes per textured polygon, 9.844 KB memory (140 polygons per frame), 151.2 KB/s bandwidth (2100 polygons/sec)

References

Sega Mega-CD Hardware
 Overview   Sega Mega-CD | Technical Specifications | History
 Hardware Variations   Wondermega | LaserActive | Sega Multi-Mega | CSD-G1M
Misc. Hardware   CD BackUp RAM Cart | Mega-CD Karaoke | Pro CDX
Development Tools SNASM Mega-CD, PsyQ Mega-CD SDK, PSY-Q CD Emulation System (Mega-CD)
Cancelled Hardware   Game Genie