Sega Mega Drive / Genesis (Model 1): Difference between revisions
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| os = None (game cartridge provides code) | | os = None (game cartridge provides code) | ||
| predecessor = [[Master System II]] | | predecessor = [[Master System II]] | ||
| successor = [[Sega | | successor = [[Sega Mega Drive / Genesis (Model 2)]] | ||
| codename = '''MK-1601''' (HAA-2510 PCB) | | codename = '''MK-1601''' (HAA-2510 PCB) | ||
| model = “VA0–VA6” motherboard revisions | | model = “VA0–VA6” motherboard revisions | ||
}} | }} | ||
The '''Sega Mega Drive'''—released as the '''Sega Genesis''' in North America—is a 16-bit fourth-generation console that propelled Sega into direct competition with Nintendo’s Super Famicom/SNES. Its Motorola 68000 CPU and sophisticated Yamaha FM audio gave arcade-like performance at home, while aggressive “Genesis does what Nintendon’t” marketing helped drive '''≈ 30 million units''' sold worldwide. | The '''Sega Mega Drive'''—released as the '''Sega Genesis''' in North America—is a 16-bit fourth-generation console that propelled Sega into direct competition with Nintendo’s Super Famicom/SNES. Its Motorola 68000 CPU and sophisticated Yamaha FM audio gave arcade-like performance at home, while aggressive “Genesis does what Nintendon’t” marketing helped drive '''≈ 30 million units''' sold worldwide. | ||
== | == Architecture & Dual-CPU Design == | ||
{| class="wikitable styled-table" style="width:70%; text-align:center;" | {| class="wikitable styled-table" style="width:70%; text-align:center;" | ||
! Sub-system !! Specification (Model 1 VA4, NTSC) | ! Sub-system !! Specification (Model 1 VA4, NTSC) | ||
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|} | |} | ||
== | == Memory Map (NTSC, no add-ons) == | ||
{| class="wikitable styled-table" style="width:70%;" | {| class="wikitable styled-table" style="width:70%;" | ||
|+'''Mega Drive Model 1 Address Space (68000)''' | |+'''Mega Drive Model 1 Address Space (68000)''' | ||
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Key ROM vectors: <code>000004</code> initial SSP, <code>000006</code> initial PC (game entry), TMSS “SEGA” string check at <code>000100</code> on later VA6(+). | Key ROM vectors: <code>000004</code> initial SSP, <code>000006</code> initial PC (game entry), TMSS “SEGA” string check at <code>000100</code> on later VA6(+). | ||
== | == Video Timing == | ||
{| class="wikitable styled-table" style="width:70%; text-align:center;" | {| class="wikitable styled-table" style="width:70%; text-align:center;" | ||
! Mode !! Pixel clock !! Pixels/line !! Lines/frame !! Refresh | ! Mode !! Pixel clock !! Pixels/line !! Lines/frame !! Refresh | ||
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|} | |} | ||
''The VDP fetches one 16-bit VRAM word every 4 cycles; HSYNC width ≈ 84 master clocks.'' | |||
== | == Edge Connector (64-pin Cartridge Slot) == | ||
{| class="wikitable styled-table" style="width:90%; text-align:center;" | {| class="wikitable styled-table" style="width:90%; text-align:center;" | ||
! Pin !! Signal !! Description !! Pin !! Signal !! Description | ! Pin !! Signal !! Description !! Pin !! Signal !! Description | ||
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|} | |} | ||
''Full 64-pin table located on the [[Mega Drive Cartridge Pin-out]] page.'' | |||
== | == Model 1 Motherboard Revisions == | ||
{| class="wikitable styled-table" style="width:80%; text-align:center;" | {| class="wikitable styled-table" style="width:80%; text-align:center;" | ||
|+'''Key Mega Drive VA-board Changes''' | |+'''Key Mega Drive VA-board Changes''' | ||
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|} | |} | ||
VA4 & later drop the “EXT PORT” text on the front but keep the 9-pin SUB-D connector. Revision affects RGB quality and capacitor layout—see the dedicated [[Sega Mega Drive Maintenance Guide|maintenance guide]] for board-specific recap lists. | VA4 & later drop the “EXT PORT” text on the front but keep the 9-pin SUB-D connector. Revision affects RGB quality and capacitor layout—see the dedicated [[Sega Mega Drive / Genesis (Model 1) Maintenance Guide|maintenance guide]] for board-specific recap lists. | ||
== | == Audio Path == | ||
68000 DMA → YM2612 FM → mixed with PSG → pre-emphasis RC filter → Sony CXA1034 op-amp → headphone amp & rear AV-out. | 68000 DMA → YM2612 FM → mixed with PSG → pre-emphasis RC filter → Sony CXA1034 op-amp → headphone amp & rear AV-out. | ||
*Early VA0/VA1 units suffer the well-known “Mega-Drive whistle.”* Installing 470 µF / 100 µF low-ESR caps and moving the audio return after the regulators mitigates it (documented in the [[Mega Drive AV Output Guide]]). | *Early VA0/VA1 units suffer the well-known “Mega-Drive whistle.”* Installing 470 µF / 100 µF low-ESR caps and moving the audio return after the regulators mitigates it (documented in the [[Mega Drive AV Output Guide]]). | ||
== | == Historical Context & Sales == | ||
* Conceived under codename '''“Mark V”''' to supersede the 8-bit Master System using Sega’s System-16 arcade silicon. | * Conceived under codename '''“Mark V”''' to supersede the 8-bit Master System using Sega’s System-16 arcade silicon. | ||
* Japanese uptake was modest (≈ 400 k units by 1990) until ''Sonic the Hedgehog'' (1991) exploded sales. | * Japanese uptake was modest (≈ 400 k units by 1990) until ''Sonic the Hedgehog'' (1991) exploded sales. | ||
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* Sixth-year production cost with VA6 board < US$50, leading to sub-£100 “Mega Drive II” bundles in 1995. | * Sixth-year production cost with VA6 board < US$50, leading to sub-£100 “Mega Drive II” bundles in 1995. | ||
== | == Common Faults & Preventive Maintenance == | ||
* '''Electrolytic capacitor leakage''' around CXA1034 (audio) and power rails (5 V, -12 V op-amp). See [[Mega Drive Capacitor Replacement Guide]]. | * '''Electrolytic capacitor leakage''' around CXA1034 (audio) and power rails (5 V, -12 V op-amp). See [[Sega Mega Drive / Genesis (Model 1) Capacitor Replacement Guide]]. | ||
* '''No video / jailbars''' – cracked solder on AV DIN, VDP or RAM ICs. | * '''No video / jailbars''' – cracked solder on AV DIN, VDP or RAM ICs. | ||
* '''RESET line stuck low''' – faulty MC14069 (Hex Schmitt inverter) on VA0-VA3. | * '''RESET line stuck low''' – faulty MC14069 (Hex Schmitt inverter) on VA0-VA3. | ||
* '''Z80 bus contention''' causes garbled FM – reseat / clean edge cartridge & check 315-5410 ASIC. | * '''Z80 bus contention''' causes garbled FM – reseat / clean edge cartridge & check 315-5410 ASIC. | ||
* Full troubleshooting flow-chart on [[Mega Drive Troubleshooting Guide]]. | * Full troubleshooting flow-chart on [[Sega Mega Drive / Genesis (Model 1) Troubleshooting Guide]]. | ||
== | == Expansion & I/O == | ||
* '''Cartridge slot''' 64-pin edge (mapped @ 0–4 MB) | * '''Cartridge slot''' 64-pin edge (mapped @ 0–4 MB) | ||
* '''EXT PORT''' 9-pin mini-DIN (unused by most games; utilised by Sega CD side-bus) | * '''EXT PORT''' 9-pin mini-DIN (unused by most games; utilised by Sega CD side-bus) | ||
* '''AV Out''' 8-pin mini-DIN (RGB 0.7 Vpp, composite, mono audio) | * '''AV Out''' 8-pin mini-DIN (RGB 0.7 Vpp, composite, mono audio) | ||
* '''Controller ports''' 2× DE-9 (compatible with Atari/VCS & MS pads) | * '''Controller ports''' 2× DE-9 (compatible with Atari/VCS & MS pads) | ||
* '''Add-ons:''' [[Sega | * '''Add-ons:''' [[Sega CD (Model 1)]] (CD-ROM storage, additional 12.5 MHz 68000 & PCM) and [[Sega 32X]] (2× Hitachi SH-2 @ 23 MHz, 32-colour cell-based renderer) | ||
== | == Trivia & Pop-culture == | ||
* Early Japanese units proudly display '''“High Definition Graphics • Stereo Sound”''' silk-screen; later cost-reduced versions removed the legend though hardware remained identical. | * Early Japanese units proudly display '''“High Definition Graphics • Stereo Sound”''' silk-screen; later cost-reduced versions removed the legend though hardware remained identical. | ||
* The console appears (model-accurate) in the 2020 film ''Sonic the Hedgehog''—complete with a VA3 style headphone volume wheel. | * The console appears (model-accurate) in the 2020 film ''Sonic the Hedgehog''—complete with a VA3 style headphone volume wheel. | ||
* An undocumented VDP test pattern can be triggered by holding <code>A+B+C+START</code> on power-up with no cartridge inserted (development boards only). | * An undocumented VDP test pattern can be triggered by holding <code>A+B+C+START</code> on power-up with no cartridge inserted (development boards only). | ||
== Further reading / guides == | |||
* [[Sega Mega Drive / Genesis (Model 1) Maintenance Guide]] – disassembly, PSU voltages, cleaning | |||
* [[Sega Mega Drive / Genesis (Model 1) Troubleshooting Guide]] – no-power, black-screen, audio issues | |||
* [[Sega Mega Drive Maintenance Guide]] – disassembly, PSU voltages, cleaning | * [[Sega Mega Drive / Genesis (Model 1) Capacitor Replacement Guide]] – board-specific recap BOM | ||
* [[Sega Mega Drive Troubleshooting Guide]] – no-power, black-screen, audio issues | |||
* [[Sega Mega Drive Capacitor Replacement Guide]] – board-specific recap BOM | |||
* [[Sega Mega Drive AV Output Guide]] – RGB, composite, stereo mod & jailbar fixes | * [[Sega Mega Drive AV Output Guide]] – RGB, composite, stereo mod & jailbar fixes | ||
<references /> | <references /> | ||
[[Category:Sega Systems]] | [[Category:Sega Systems]] | ||