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) cpu 68000 the 68000 cpu is responsible for most of the work on the console including running mega drive games co processor z80 cpu 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 video display processor this custom sega ic 315 5313 controls video output generation, reading data from both the cpu and co processor, utilizing the video dram bus arbiter 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 this 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 this 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 io controller 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 clock generator 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 this 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 this 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 audio processor 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 audio amplifier the cxa1034p audio amplifier is used to output audio to the headphone port video encoder 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