This information is collaboratively maintained here:

S8Dev:Pinouts-Index

This page remains only as a remnant of my original investigations.

Disclaimer

The information on this page is accurate as far as I know but I make no guarantee. I am very interested to know of any mistakes I may have made.

Sega Master System, outside Japan/Korea, cartridge port pinouts

Sega Master System cartridge port pinouts

The ordering of the address and data pins allows for simple connection to common ROM and EPROM chips.

Sega Master System expansion port pinouts

Sega Master System expansion port pinouts

Note that the pin connections exactly match those of the export Master System cartridge port, with the front connections on the lower edge.

Sega SG-1000, SC-3000, Mark III, Japanese Master System cartridge port pinouts

Sega SG-1000, SC-3000, Mark III, Japanese Master System cartridge port pinouts

Note that the SG-1000 and SC-3000 have the same connector worldwide.

The function of pin B9 is uncertain at present. It may be CE, Refresh or NC.

Korean variants such as the Gam*Boy have the same connector.

Sega SG-1000, SC-3000, Mark III expansion port pinouts

Sega SG-1000, SC-3000, Mark III expansion port pinouts

Some of the lines are not connected on earlier hardware revisions such as the SG-1000.

Sega Master System/Mark III card port pinouts

Sega Master System/Mark III card port pinouts

These are in the same order as the export SMS cartridge port.

Sega Game Gear cartridge port pinouts

Sega Game Gear cartridge port pinouts

These are also similar to the export SMS cartridge port.

Pin descriptions

Some of the abbreviated labels on the pins are harder to understand than others. Here’s a description of their functions.

Pin labelDirectionMeaning
A0..A15OAddress lines. Used to select a 16-bit location in memory, or an 8-bit I/O port.
D0..D7I/OData lines. 8-bit data is transferred here.
 
RdONot read. 0 when the CPU is reading from the data bus, 1 otherwise.
WrONot write. 0 when the CPU is writing to the data bus, 1 otherwise.
MReqONot memory request. 0 when the address bus specifies a memory location, 1 otherwise.
IOReqONot I/O request. Set to 0 when the address bus specifies an I/O address.
ClockONot clock. Pulses from 1 to 0 once per machine clock cycle (3.5MHz).
IntINot interrupt. When set to 0, the Z80 will execute an interrupt request (if enabled) after the current opcode.
NMIINot non-maskable interrupt. When it switches from 1 to 0, the Z80 will execute an NMI (rst $66).
M1ONot machine cycle 1. 0 when the CPU is fetching an opcode, 1 when it is decoding and executing.
RefreshONot refresh. Used for refreshing DRAM memory chips.
HaltONot halt. The Z80 sets it to 1 when it is executing a halt opcode.
WaitINot wait. Set to 0 by an external device to signal that data is not ready to be read from the bus yet.
BusAckONot bus acknowledge. Becomes 0 when the Z80 has yielded the bus in response to a BusReq signal.
BusReqINot bus request. Setting it to 0 will cause the Z80 to suspend operation and allow an external device to access the bus.
 
CEONot chip enable. 0 when the cartridge (or card, or slot) is enabled, 1 otherwise.
ResetONot reset. Changes from 1 to 0 to reset any attached hardware, such as mapper chips, when the system starts.
KBSELONot keyboard select. 0 when the keyboard/joystick port region ($40-$5f, $c0-df) is being accessed.
JReadOJoystick read. 1 when the joystick port region ($c0-$ff) is being accessed. May be active-low logic and thus equivalent to KBSEL.
JyDsIJoystick disable. 1 when joystick output has been disabled, 0 otherwise. This corresponds to bit 2 of port $3E as set by the software. It can be used by an FM expansion pack to tell when joysticks have been disabled, which happens before the FM chip is accessed.
M0-7ONot memory $0000-$7fff. 0 when the address is in this range, 1 otherwise.
M8-BONot memory $8000-$bfff. 0 when the address is in this range, 1 otherwise.
MC-FONot memory $c000-$ffff. 0 when the address is in this range, 1 otherwise.
CSCN4INot connector 4 chip select. Setting it to 1 will disable connector 4, which I think means the Mark III card slot. It is normally tied to +5V by the cartridge.
CSRAMINot RAM chip select. Setting it to 1 will disable on-board RAM, allowing the cartridge to use the $c000-$ffff region. Also known as RAMKILL.
CONTIA general-purpose input bit that can be read from port $dd, in later hardware it instead represents the Reset button state.
 
RAS0OThese are all related to DRAM refreshing, and are used for the on-cartridge RAM in BASIC cartridges.
RAS1O...
CAS0O...
CAS1O...
CA7O...
RCSELO...
 
+5V-Power, represents binary 1. Logic chips generally require both Ground and +5V for reference to work.
Gnd-Ground (0V), represents binary 0.
 
+34V-The high-voltage supply for the Game Gear’s fluorescent tube LCD backlight.
GGISet to 0 for Game Gear mode, 1 for SMS mode.
TVISet to 0 to remap the cartridge port for digital video input from the TV Tuner device. Set to 1 for regular usage.
TV LIAnalogue audio inputs for the TV Tuner device.
TV RI...

Connections needed for a convertor

You need to connect these lines as a bare minimum:

  • A0-A15
  • D0-D7
  • Rd
  • Wr
  • +5V
  • Gnd
  • M0-7 (connect to A15 if unavailable)
  • M8-B
  • CE (or MReq)

In general, connect MReq to MReq and CE to CE if possible; if the source does not have a CE line then connect MReq instead.

The following lines are not present on all connectors but should also be joined if available:

  • MC-F
  • M1
  • Refresh
  • Reset
  • Clock

Some games will not work without some of these additional connections.

Any further pins with identical labels in the diagrams may be connected but may not be needed. Below are some examples of existing adaptors, known to work.

Island Trade Adaptor (export SMS to Mark III/Japanese SMS)

Cartridge pinSlot pin
A0-A15A0-A15
D0-D7D0-D7
+5V,Reset+5V,CSCN4
GndGnd
RdRd
WrWr
CEMReq
M0-7A15
M8-BM8-B

It also connects CONT to +5V but this is unnecessary. It also connects the cartridge’s MReq line to B9 which seems to be incorrect.

Master Gear Adaptor (export SMS to Game Gear)

Cartridge pinSlot pin
A0-A15A0-A15
D0-D7D0-D7
+5V+5V,GG,TV
GndGnd
RdRd
WrWr
M0-7M0-7
M8-BM8-B
CECE
M1M1
RefreshRefresh
ResetReset
ClockClock

If you also connect the SMS’s MReq pin to the GG’s CE pin, you will reportedly gain compatibility with Codemasters games and possibly also the SMS-Pro flash cartridge.

NOTE: If you are making a GG -> SMS adaptor (e.g. for dumping cartridges), leave the GG pin (pin 42) disconnected.

Mark III/Japanese SMS to Game Gear adaptor

Based on the Island Trade Adaptor and Master Gear connection information, Yujiro made this.

Cartridge pinSlot pin
A0-A15A0-A15
D0-D7D0-D7
+5V,Reset+5V
GndGnd
RdRd
WrWr
M0-7A15
M8-BM8-B
CEMReq

Export SMS to Japanese/export SMS expansion port adaptor

The Japanese Master System has the same expansion port connector as export systems, which exactly matches the pinout of export Master System cartridges (although inverted). Bock and others made a guide for connecting these:

Sega Master System gender adaptor

All-in-one diagram

You can download all of the pinout diagrams in one PNG file, with no colour reduction (330KB).

Credits

These images and the accompanying text was written by Maxim but is based on the information provided by, comments of and questions answered by Charles MacDonald, Asynchronous, Enri, Richard Atkinson, Bock, Sankichi, Richard Aplin, Yujiro and maybe more.

Corrections?

Go and edit from S8Dev:Pinouts-Index.