Sega Master System (Model 1): Difference between revisions
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=== Exact 64 KB CPU Memory-Map (Model 1) === | === Exact 64 KB CPU Memory-Map (Model 1) === | ||
{| class="wikitable styled-table" style="width: | {| class="wikitable styled-table" style="width:70%; text-align:center;" | ||
|+''Z80 Address Space'' | |+''Z80 Address Space'' | ||
! Range !! Size !! Purpose / Notes | ! Range !! Size !! Purpose / Notes | ||
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''Mapper registers'' are written through bogus addresses $FFFC–$FFFF (upper bits decoded by on-cart ASICs such as 315-5196). | |||
=== BIOS Entry Points (v1.3) === | === BIOS Entry Points (v1.3) === | ||
Revision as of 10:08, 27 April 2025
| File:Sega-Master-System-MK-2000.jpg | |
| First-generation «Master System» console (MK-2000, 1986) with cartridge & Sega Card slots | |
| Specifications | |
|---|---|
| Manufacturer | Sega Enterprises, Ltd. |
| Type | Home video-game console |
| Released |
|
| Discontinued |
|
| Intro price | US$199 (NA launch bundle, 1986) |
| CPU | Zilog Z80A @ 3 579 545 Hz (NTSC) / 3 546 895 Hz (PAL) |
| Memory | 8 KB work-RAM • 16 KB video-RAM |
| Storage | ROM cartridges (max 4 Mbit) • Sega Card (256 Kbit) • optional FM sound BIOS (Japan) |
| Display | VDP 315-5124/5246 → 256 × 192 (nom.) / 32-colour on-screen from 64-colour palette |
| Sound | SN76489-compatible PSG (3 square + 1 noise) • optional YM2413 FM add-on (JP) |
| Dimensions | 365 mm W × 170 mm D × 66 mm H |
| Weight | ≈ 2.1 kg |
| OS / Firmware | None (8 KB BIOS v1.3 – menu + hidden Snail Maze) |
| Predecessor | Sega SG-1000 II |
| Successor | Sega Mega Drive |
| Codename | Mark III |
| Model no. | MK-2000 / MK-3000 |
The Sega Master System (first-generation “Model 1”, product code MK-2000) is an 8-bit home console released by Sega to compete directly with Nintendo’s Famicom/NES. Re-branded from the Japan-only Sega Mark III, the Master System introduced the distinctive black-and-red industrial design, a combo cartridge + “Sega Card” slot, and an edge expansion port supporting FM audio, 3-D glasses and future accessories. Although outsold by Nintendo in Japan & North America, it enjoyed major success across Europe, Brazil and Australasia, shipping an estimated ≈ 13 million units worldwide.
🧠 System Architecture
| Sub-system | Specification (Master System Model 1) |
|---|---|
| CPU | Z80A 8-bit @ 3.58 MHz (NTSC) / 3.55 MHz (PAL) • 16-bit address – 64 KB space |
| VDP | Sega 315-5124 (NTSC) / 315-5246 (PAL)
TMS9918-derived: 2× pattern tables, 32 sprites (8 per scan-line) VRAM 16 KB (dual 8 KB SRAM, 5 ns page registers) |
| Palette | 64 colours (6-bit RGB) – 32 on-screen (background & sprite) |
| Audio | TI SN76489 PSG (integrated into VDP) – 3 square + 1 noise
Expansion pin-out for YM2413 FM (used in JP “FM Unit” & Mark III) |
| Main RAM | 2 × 8 KB HM6264 (work-RAM) @ ~150 ns |
| Cartridge ROM | Up to 4 Mbit/512 KB (LoROM/HiROM mapper chips: Sega 315-5235, 315-5208, etc.) |
| BIOS | 8 KB mask ROM ver 1.3 (NA/EU) — intro menu + hidden Snail Maze (hold ↑+1+2) |
| I/O | 2× DE-9 game-pad, RF-UHF & 8-pin AV, Card slot (36-pin), 50-pin cart, 35-pin EXT |
Exact 64 KB CPU Memory-Map (Model 1)
| Range | Size | Purpose / Notes |
|---|---|---|
| $0000 – $3FFF | 16 KB | ROM–0 (Cartridge / Card / BIOS) |
| $4000 – $7FFF | 16 KB | ROM–1 (bank-selectable via mapper) |
| $8000 – $BFFF | 16 KB | ROM–2 (bank-selectable) |
| $C000 – $DFFF | 8 KB | Work-RAM (on-board) |
| $E000 – $FFFF | 8 KB | Mirror of $C000 – $DFFF |
Mapper registers are written through bogus addresses $FFFC–$FFFF (upper bits decoded by on-cart ASICs such as 315-5196).
BIOS Entry Points (v1.3)
| Address | Routine |
|---|---|
| $0000 | Soft reset → Sega splash & checksum |
| $00A8 | PSG mute / init |
| $0150 | Card detect loop |
| $0200 | Hidden game “Snail Maze” (activate ↑+1+2 at logo) |
📺 Video Timing
| Parameter | NTSC | PAL |
|---|---|---|
| Master clock | 10.738635 MHz | 10.644606 MHz |
| Pixel clock | 5.369 MHz | 5.322 MHz |
| Lines/frame | 262 | 313 |
| Refresh | 59.92 Hz | 49.70 Hz |
🔌 Edge-Connector Pin-out
50-pin Cartridge Bus (looking into console)
| Pin | Signal | Description | Pin | Signal | Description |
|---|---|---|---|---|---|
| 1 | GND | Ground | 26 | A11 | Address 11 |
| 2 | +5 V | +5 V DC | 27 | A9 | Address 9 |
| 3 | CLOCK | M-clock (5.37 MHz) | 28 | A8 | |
| 4 | A15 | Address 15 | 29 | A13 | |
| 5 | A14 | Address 14 | 30 | A7 | |
| 6 | A12 | Address 12 | 31 | A6 | |
| 7 | /MREQ | Z80 Memory Request | 32 | A5 | |
| 8 | /IORQ | I/O Request | 33 | A4 | |
| 9 | /RD | Read strobe | 34 | A3 | |
| 10 | /WR | Write strobe | 35 | A2 | |
| 11 | D7 | Data 7 | 36 | A1 | |
| 12 | D6 | Data 6 | 37 | A0 | |
| 13 | D5 | Data 5 | 38 | CE (low) | |
| 14 | D4 | Data 4 | 39 | +5 V | |
| 15 | D3 | Data 3 | 40 | /BUSREQ (rarely used) | |
| 16 | D2 | Data 2 | 41 | PAUSE (pulled-up: cartridge can assert) | |
| 17 | D1 | Data 1 | 42 | /RESET | |
| 18 | D0 | Data 0 | 43 | AUDIO IN (FM/stereo mods) | |
| 19 | M1 | Op-code fetch | 44 | /NMI (3-D glasses) | |
| 20 | RFSH | Refresh | 45 | GND | |
| 21 | /HALT | CPU halt | 46 | GND | |
| 22 | A10 | Address 10 | 47 | +5 V | |
| 23 | - | (n/c) | 48 | +5 V (cart power) | |
| 24 | - | (n/c) | 49 | - | |
| 25 | A16 | Address 16 (mapper) | 50 | - |
📜 Historical Context & Sales
- 1985 – Sega launches the Mark III in Japan; hardware overhaul of the SG-1000 line.
- 1986 – Re-packaged for North America as the “Sega System”, quickly re-branded Master System under Tonka; bundled with Hang-On/Safari Hunt combo cartridge.
- 1987–1992 – Becomes the dominant 8-bit console across Europe, distributed by Virgin Mastertronic; library balloons to 300+ PAL titles.
- Brazil – Tec Toy begins local production (1989) and continues updated revisions into the 2020s; > 8 million units sold in Brazil alone.
Global lifetime sales are estimated at ≈ 13 million (vs ~62 M NES).
🔧 Maintenance & Common Faults
- Cracked solder on AV DIN → intermittent video.
- 7805 regulator runs hot (VA2 boards) – recap & replace thermal pad.
- Dying 315-5216 I/O ASIC causes random controller dropouts.
Detailed procedures: see Sega Master System General Maintenance, Sega Master System Troubleshooting Guide, Sega Master System Capacitor Replacement Guide and Sega Master System AV Output Modifications.
🔄 Board Revisions & Known Errata
| Rev | Region (year) | Notes / quirks |
|---|---|---|
| VA0 | JP (1985) | Mark III PCB – discrete VDP/PSG, no BIOS, external FM Unit |
| VA2 | NA/EU (1986) | First “Master System” – large RF can, 8 KB BIOS v1.3, 5 × 5 V regulators; early units prone to jail-bar video (unscreened VRAM lines) |
| VA3 | EU (1987) | Card slot EMI shield deleted, improved RF modulator |
| VA5 | EU (1989) | 315-5246 PAL VDP, YM2413 traces removed; RGB DIN 8 output added |
| VA6 | BR (1991) | Tec Toy – onboard TMSS lockout stub, composite only (no RF) |
🎲 Game Media
- ROM Cartridges up to 512 KB; larger titles employ paging ASICS (315-5208, 315-5235).
- Sega Card thin 35 g card, limited to 32 KB/256 Kbit – discontinued 1989.
- FM soundtrack detected via mapper bit 6; Western carts often contain unused FM data later unlocked by community patches.
🎯 Trivia & Pop-Culture
- Hidden “Snail Maze” game embedded in BIOS v1.3 – launch by holding ↑ + 1 + 2 at the Sega logo.
- Original Japanese unit’s 3-D glasses used active shutter synced via the /NMI pin; later re-used on Mega Drive add-ons.
- The console appears in Charlie Brooker’s _Black Mirror_ episode “Bandersnatch” (retro game-dev setting).
- Tec Toy released Brazilian-exclusive ports: Street Fighter II, Mônica no Castelo do Dragão (Wonder Boy II reskin), sustaining the platform into the late 1990s.
📚 Further Reading
- Sega Master System Service Manual (1986) – Part #420-5718-01
- Chris Covell, “SMS VDP documentation & palette research” (covell.ski)
- Charles MacDonald, “Master System Hardware Notes” (github.com/CharlesMacDonald)