Hardware Overview (Sega Mega Drive)
The Mega Drive circuit is mostly made up of the following chips:
- 68000 CPU (Motorola MC68000)
- SRAM for 68000 (TC51832SPL-10)
- Mega Drive VDP (315-5313)
- Video DRAM for VPD (MB81461)
- Co-Processor Z80 CPU (Zilog Z80)
- Bus Arbiter (315-5308)
- IO Controller (315-5309)
- Clock Generator (315-5345)
- Audio Processor (YM2612)
- Audio Amplifier (CXA1034P)
- Video Encoder (CXA1145)
The 68000 CPU is responsible for most of the work on the console including running Mega Drive games.
The Z80 was the CPU from the Master System and was included in the Mega Drive primarily to support backwards compatibility.
It also handles audio and controller input.
This custom Sega IC 315-5313 controls video output generation, reading data from both the CPU and Co-Processor, utilizing the video DRAM
The custom Sega IC 315-5308 holds the Z80's bank register used to select the appropriate 68k bank, whose address this chip puts on the bus during free cycles. It basically interfaces communication between the 68000 CPU and the Z80 Co-Processor.
īģŋThis chip is not present on most Mega Drive consoles it got integrated into the 315-5364 chip, which was a combination of the Bus Arbiter 315-5308 and the Clock Generator 315-5345 into a single chip.īģŋ
The main job of the Sega IC 315-5308 is as an IO Controller for translating data between the Z80 (8 bit) and 68000 (16 bit) CPUs, as well as handling controller input.
The custom Sega IC 315-5345 is responsible of EDCLK generation (external dot clock in H40 mode, based on HSYNC and MCLK inputs) and 68k RAM refresh.
īģŋThis chip is not present on most Mega Drive consoles it got integrated into the 315-5364 chip, which was a combination of the Bus Arbiter 315-5308 and the Clock Generator 315-5345 into a single chip.īģŋ
The YM2612 audio processor handled all the audio on the Mega Drive.
The YM2612, a.k.a. OPN2, is a sound chip developed by Yamaha. It is a member of Yamaha's OPN family of FM synthesis chips, and is derived from the YM2203.
The YM2612 is a six-channel FM synthesizer. It was used in several game and computer systems, most notably in Sega's Mega Drive/Genesis video game console as well as Fujitsu's FM Towns computer series.
As with the YM3438, it was used by Sega in various arcade game systems, including the Mega-Play and Sega System 32.
The CXA1034P audio amplifier is used to output audio to the headphone port.
The CXA 1145 encoder from Sony converts an analog RGB signal to a composite video signal (PAL/NTSC). With its built-in circuit various pulses required for an encoder, composite video outputs are obtained just by inputting the composite sync and analog RGB signal.
