Mega Drive official documentation
From Sega Retro
Genesis Software Development Manual
Genesis Software Development Manual 2.0
Genesis Technical Overview
Sega Service Manual - Genesis II - Mega Drive II (PAL) - 001 - June 1993
Sega Service Manual Supplement - Genesis II - Mega Drive II (PAL) - 001-1 - August 1993
Sega Service Manual Supplement - Genesis II - Mega Drive II (PAL) - 001-2 - December 1993
Sega Service Manual - Genesis II VA3 - 001-3 - August 1994
Sega Service Manual Parts Specifications - Genesis VA7 - Mega Drive PAL VA6.5 - Mega/Sega CD - 010 - April 1994
The Sega Development System (Accolade) 21 February 1991
Accolade Sound Document - 3 November 1990
Accolade Z80 Document - 1
Accolade Z80 Document - 2
INIT.ASM - Accolade's Sega Initialisation Program - 13 March 1991