Sega Mega Drive/Hardware revisions

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Model 1

	VA0 (JPN)
	Components: M68K CPU: Signetics SCN68000C8N64 M68K memory: 2x HM65256BLSP-15 (32Kx8 PSRAM, 150 ns) Z80 CPU: Zilog Z0840004PSC Z80 memory: TMM2063P - 10 (8Kx8 SRAM, 100 ns) I/O chips: Sega 315-5308, Sega 315-5309, Signectic 74LS00N, 74LS161AN, 74F161AN, 74LS74AN (DIP-16) VDP: Sega 315-5313 (Yamaha YM7101) Video RAM: 2x HM53461ZP-12 (64Kx4 VRAM 120 ns) Headphone amp: Sony CXA1034 Video encoder: Sony CXA1145 FM synthesizer: Yamaha YM2612 Due to a last-minute issue with the VDP in H40 mode, additional clock circuitry had to be added during manufacturing. This circuitry is present on a daughterboard in the center of the PCB, and contains the master oscillator (53.6931 MHz, NTSC), a 74LS74 (dual D-type flip-flops), and two 74LS161s (4-bit counter). An issue in the hardware causes the RAM memory to not completely initialize when the game starts, causing crashes in Osomatsu-kun Hachamecha Gekijou.
	VA1 (JPN)
	Components: M68K CPU: Signetics SCN68000C8N64 M68K memory: 2x TC51832SPL-10 (32Kx8 PSRAM, 100 ns) Z80 CPU: Zilog Z0840004PSC Z80 memory: NEC D4168C-20 (8Kx8 XRAM, 200 ns) I/O chips: Sega 315-5308, Sega 315-5309, Sega 315-5339 (DIP-16) VDP: Sega 315-5313 (Yamaha YM7101) Video RAM: 2x HM53461ZP-12 (64Kx4 VRAM 120 ns) Headphone amp: Sony CXA1034 Video encoder: Sony CXA1145 FM synthesizer: Yamaha YM2612 Capacitors : TK Japan
	VA2 (USA, High Definition Graphics)
	Components: M68K CPU: Signetics SCN68000C8N64 M68K memory: 2x TC51832SPL-12 (32Kx8 PSRAM, 120 ns) Z80 CPU: Zilog Z0840004PSC Z80 memory: NEC D4168C-15 (8Kx8 XRAM, 150 ns) I/O chips: Sega 315-5308, Sega 315-5309, Sega 315-5345 (DIP-16) VDP: Sega 315-5313 (Yamaha YM7101) Video RAM: 2x [NUMBER PLEASE] (64Kx4 VRAM) Headphone amp: Sony CXA1034 Video encoder: Sony CXA1145 FM synthesizer: Yamaha YM2612
	VA3 (USA, High Definition Graphics)
	Components: M68K CPU: Motorola MC68000P8 M68K memory: 2x HM65256BL-10 (32Kx8 PSRAM, 100 ns) Z80 CPU: Zilog Z0840004PSC Z80 memory: KM6264BL-10 (8Kx8 SRAM, 100 ns) I/O chips: Sega 315-5309, Sega 315-5364 VDP: Sega 315-5313 (Yamaha YM7101) Video RAM: KM424C64Z-10, VKF015 (64Kx4 VRAM) Headphone amp: Sony CXA1034 Video encoder: Sony CXA1145 FM synthesizer: Yamaha YM2612 Capacitors : Taicon, Chhsi
	VA4 (JPN)
	Components: M68K CPU: Signetics SCN68000C8N64 M68K memory: 2x TC51832SP-12 Z80 CPU: Zilog Z0840004PSC Z80 memory: NEC D4168C-15-SG I/O chips: Sega 315-5364, Sega 315-5309 VDP: Sega 315-5313 (Yamaha YM7101) Headphone amp: Sony CXA1034P Video encoder: Sony CXA1145P FM synthesizer: Yamaha YM2612
	VA4 (PAL)
	Components: M68K CPU: Motorola MC68000P8 M68K memory: Hitachi HM65256BLSP-10 (32Kx8 PSRAM, 100 ns) I/O chip: Sega 315-5364, Sega 315-5309 Z80 CPU: Zilog Z0840004PSC Z80 memory: Sanyo LC3664RL (8Kx8 SRAM, 120 ns) VDP: Sega 315-5313 (Yamaha YM7101) Video RAM: Fujitsu MB81461-12 (64Kx4 VRAM) Headphone amp: Sony CXA1034P Video encoder: Sony CXA1145P RGB Encoder FM synthesizer: Yamaha YM2612 Dual Operational Amplifier: Ti LM358P
	VA5 (JPN)
	VA6 (JPN)
	The first Japanese revision with the TMSS.
	VA6 (USA, High Definition Graphics)
	Components: M68K CPU: Motorola MC68000P8 M68K memory: 2x HM652568LSP-10 (32Kx8 PSRAM, 100 ns) Z80 CPU: Zilog Z0840004PSC Z80 memory: MB8464A-10 (8Kx8 SRAM, 100 ns) I/O chip: Sega 315-5433 VDP: Sega 315-5313 (Yamaha YM7101) Video RAM: 2x [NUMBER PLEASE] (64Kx4 DRAM) Headphone amp: Sony CXA1034 Video encoder: Sony CXA1145P FM synthesizer: Yamaha YM2612
	VA6.5 (PAL)
	The unused female DE-9 port (used for the Mega Modem in Japan) is removed.
	VA6.8
	VA7 (USA)
	Components: M68K CPU: Motorola MC68HC000FN8 M68K memory: 2x 65256BLFP-10T Z80 CPU: Zilog Z0840004PSC Main ASIC: Sega 315-5487-01 Headphone amp: BA10324AF Video encoder: Sony CXA1145M FM synthesizer: Yamaha YM2612 (ASIC YM3438) This revision is similar to the VA0 revision of the Model 2, in which it has a different M68K CPU and memory chips, as well as the main ASIC and audio amplifiers. The only difference is the Z80 CPU, which is in the same design used with the rest of the Model 1 revisions. A function on the VDP (integrated into the ASIC) has broken PAL 50Hz support.

Model 2

	VA0 (JPN)
	The YM2612 is now based on the YM3438, and is integrated into the main ASIC (the Sega 315-5487-10).
	VA0 (PAL)
	VA0 (USA)
	Components: M68K CPU: Hitachi HD68HC000CP8 M68K memory: Toshiba TC51832AFL-10 Z80 CPU: Toshiba 84C00AU-6 Main ASIC: Sega 315-5487-01 Video Encoder: Samsung KA2195D Amplifier: Texas Instruments 311223J
	VA1 (USA)
	VA1 (PAL)
	Components: M68K CPU: Motorola MC68HC000FN8 M68K memory: Sanyo LC331632M-12 Z80 CPU: Toshiba 84C00AU-6 Main ASIC: Sega 315-5660 Video Encoder: Fujitsu MB3514 Amplifier: BA10324AF
	VA1.8 (USA)
	PCB Printed by SKS Components: M68K CPU: Motorola MC68HC000FN8 M68K memory: Sanyo LC36648ML-10 Z80 CPU: Toshiba 84C00AU-6 Main ASIC: Sega 315-5660-02 Video Encoder: Samsung KA2195D Amplifier: BA10324AF
	VA1.8 (USA)
	PCB Printed by CMK Components: M68K CPU: Motorola MC68HC000FN8 M68K memory: Sanyo LC331632M-12 Z80 CPU: Zilog Z84C0006FEC Main ASIC: Sega 315-5660 Video Encoder: Samsung KA2195D Amplifier: BA10324AF
	VA1.8 (PAL)
	Components: M68K CPU: Motorola MC68HC000FN8 M68K memory: ??? 651632DFP-15 Z80 CPU: Zilog Z84C0006FEC Main ASIC: Sega 315-5660 Video Encoder: Fujitsu MB3514 Amplifier: BA10324AF
	VA1.8 (Asia)
	Components: M68K CPU: Motorola MC68HC000FN8 M68K memory: Toshiba TC511632FL-10 (32Kx16 PSRAM, 100 ns) Z80 CPU: Toshiba 84C00AU-6 Z80 memory: [NUMBER PLEASE] (8Kx8 SRAM) Main ASIC: Sega 315-5660 Amplifier: BA10324AF
	VA2 (USA)
	Components: M68K CPU: Motorola MC68HC000FN12 M68K memory: Sanyo LC331632M-12 Z80 CPU: Zilog Z84C0006FEC Main ASIC: Sega 315-5786 Amplifier: Sega 315-5684 FM synthesizer: Yamaha YM2612 This revision (along with the VA2.3) is the only Model 2 boards with a discrete YM2612 chip. Additional circuitry is present on the daughterboard located on the PCB, with model number 171-6961A.
	VA2.3 (USA)
	Components: M68K CPU: Motorola MC68HC000FN12 M68K memory: Toshiba TC511632FL-10 (32Kx16 PSRAM, 100 ns) Z80 CPU: Zilog Z84C0006FEC Z80 memory: KM78128LG-7 (8Kx8 SRAM) Main ASIC: Sega 315-5685 Video Encoder: Sony CXA1645M Amplifier: Sega 315-5684 FM synthesizer: Yamaha YM2612 This revision (along with the VA2) is the only Model 2 boards with a discrete YM2612 chip.
	VA3
	Components: M68K CPU: Motorola MC68HC000FN12 M68K memory: ??? 651632DFP-15 Z80 CPU: Zilog Z84C0006FEC Main ASIC: Sega 315-5660 Video Encoder: Sony CXA1645M Amplifier: Sega 315-5684
	VA4
	Components: IC1: Sega 315-5960 ASIC IC2: 32Kx16 PSRAM IC3: Video RAM? IC4: Sega 315-5684 audio amplifier IC5: Sony CXA1645M video encoder IC6: 7805 voltage regulator This is the first Mega Drive board without any discrete CPUs. Both the 68000 and Z80 are contained with the Sega 315-5960 ASIC, as well as the VDP, YM3438, and I/O controllers.

Model 3

	VA1 (USA)
	Components: IC1: Sega 315-5960 ASIC (see above) IC2: Sharp LH5P1632N-15 32Kx16 PSRAM IC5: OKI M54C864-80 512K (64K x 8-bit) VRAM IC6: Sony CXA1645M RGB Encoder IC7: TI LM324 amplifier IC3 and IC4 markings are silkscreened but don't correspond to any physical ICs.
	VA2 (USA)
	Components: Main ASIC: Sega 315-6123 (contains M68K, Z80, VDP, YM3438, and probably some other components.) Memory (right of main ASIC): NEC D4502161G5 (128Kx16 SDRAM) Oscillator (bottom-right of main ASIC): SG53 PTR S 53.6931M Video Encoder (bottom-left of main ASIC): Sony CXA1645M Amplifier (left of main ASIC): TI 85AFTRF LM324 The tas function of the M68K (which was broken in prior revisions) has been fixed in this revision, making some games such as Gargoyles unplayable.