Sega Master System

Input/Output Ports

I/O space mapped ports

Starting port	Ending port	Read	Write	Origin	Description
0x3E	0x3E	No	Yes	Sega Master System	Memory control port
0x3F	0x3F	Yes	Yes	Sega Master System	I/O control port
0x40	0x7F	No	Yes	Sega SG-1000	PSG control port
0x80	0x80	Yes	Yes	Sega SG-1000	VDP data port
0x81	0x81	Yes	Yes	Sega SG-1000	VDP control port
0xC0	0xC0	Yes	No	Sega SG-1000	Controller A input port
0xC1	0xC1	Yes	No	Sega SG-1000	Controller B input port
0xF0	0xF1	No	Yes	Sega Mark III	YM2413 OPLL control ports
0xF2	0xF3	Yes	Yes	Sega Mark III	Audio control port

The Sega Master System is part of the SG-1000 family of video game consoles. As such, it has a high degree of compatibility with its predecessors, the SG-1000 and the Mark III. There are, however a few things to have in account. Only Japanese Sega Master System has the FM hardware, so ports 0xF0-0xF3 are unavailable to European and American models; lectures to port 0xF2 has to be done repeteadly in order to avoid false detections. Also, Mark III and Japanese Master Systems differ in how they enable the FM hardware: while in the older console the PSG and the FM hardware are mutually exclusive, its successor had an enable logic that could have both subsystems enabled at the same time. There are differences on how Japanese consoles and export ones manage port 0x3F, therefore region can be recognized by writing and reading that port.

Memory space mapped ports

Address	Read	Write	Description
0xFFFD	Yes*	Yes	Slot 0 (0x0400-0x3FFF) bank
0xFFFE	Yes*	Yes	Slot 1 (0x4000-0x7FFF) bank
0xFFFF	Yes*	Yes	Slot 2 (0x8000-0xBFFF) bank

There is an official Sega mapper that divides the address space in three slots and RAM. The bank used in each slot is determined by three write only registers at 0xFFFD-0xFFFF, however, as their placement collides with the in-system RAM they can be read back.

Units in collection

ID	Model	Comments
211	Master System	V4
212	Master System	V2
213	Master System	V3

See also

Sega 8-bit resources