The SEGA Genesis (US) / Mega Drive (everywhere else) was a 1988 game console, known for great arcade ports, FM sound, and impressive 2D graphics. It had a Motorola 68000 CPU, 64 KB main RAM, and 64 KB Video RAM. One of the most well-known games for the system is Sonic the Hedgehog, developed by SEGA and released in 1991. This page contains a series of articles about this hardware, including how to program for it, starting from the very basics.
SEGA Genesis: Building a ROM 2017-06-11
Getting started with SEGA Genesis development, and building a ROM that will run on an emulator.
SEGA Genesis: Characters and Playfields 2017-08-06
A description of the basic building blocks of Genesis graphics, and how they are put together to form screen images. 8x8 16-color tiles are mapped to form playfields. A couple of games are analyzed, including some more advanced techniques, usable for rendering polygons.
SEGA Genesis: Video Display Processor 2017-08-01
A SEGA Genesis graphics tutorial, that explains how to access the 'Video Display Processor' (VDP) graphics processor.
SEGA Genesis: Printing Text 2017-09-10
Building on the previous entry, it is explained how the VDP can be used to output text to the screen. This includes creating a font, loading it to graphics memory, writing character indices to playfields, and wrapping it into a useful subroutine.
SEGA Genesis: Code Structure 2018-07-16
A few examples of assembly code structure is explored, including variables, arrays and structures, function calling conventions, and how to implement the State Pattern.
SEGA Genesis 
Genesis hardware 
Tile graphics (Zombies Ate My Neighbours) 
Contra: Hard Corps 
Text output 
Thunderforce 4 
Menu 
Contra: Hard Corps ROM chip