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
|