This information is collaboratively maintained here:
This page remains only as a remnant of my original investigations.
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
The ordering of the address and data pins allows for simple connection to common ROM and EPROM chips.
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
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
Some of the lines are not connected on earlier hardware revisions such as the SG-1000.
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
These are also similar to the export SMS cartridge port.
Some of the abbreviated labels on the pins are harder to understand than others. Here’s a description of their functions.
|A0..A15||O||Address lines. Used to select a 16-bit location in memory, or an 8-bit I/O port.|
|D0..D7||I/O||Data lines. 8-bit data is transferred here.|
|Rd||O||Not read. 0 when the CPU is reading from the data bus, 1 otherwise.|
|Wr||O||Not write. 0 when the CPU is writing to the data bus, 1 otherwise.|
|MReq||O||Not memory request. 0 when the address bus specifies a memory location, 1 otherwise.|
|IOReq||O||Not I/O request. Set to 0 when the address bus specifies an I/O address.|
|Clock||O||Not clock. Pulses from 1 to 0 once per machine clock cycle (3.5MHz).|
|Int||I||Not interrupt. When set to 0, the Z80 will execute an interrupt request (if enabled) after the current opcode.|
|NMI||I||Not non-maskable interrupt. When it switches from 1 to 0, the Z80 will execute an NMI (rst $66).|
|M1||O||Not machine cycle 1. 0 when the CPU is fetching an opcode, 1 when it is decoding and executing.|
|Refresh||O||Not refresh. Used for refreshing DRAM memory chips.|
|Halt||O||Not halt. The Z80 sets it to 1 when it is executing a halt opcode.|
|Wait||I||Not wait. Set to 0 by an external device to signal that data is not ready to be read from the bus yet.|
|BusAck||O||Not bus acknowledge. Becomes 0 when the Z80 has yielded the bus in response to a BusReq signal.|
|BusReq||I||Not bus request. Setting it to 0 will cause the Z80 to suspend operation and allow an external device to access the bus.|
|CE||O||Not chip enable. 0 when the cartridge (or card, or slot) is enabled, 1 otherwise.|
|Reset||O||Not reset. Changes from 1 to 0 to reset any attached hardware, such as mapper chips, when the system starts.|
|KBSEL||O||Not keyboard select. 0 when the keyboard/joystick port region ($40-$5f, $c0-df) is being accessed.|
|JRead||O||Joystick read. 1 when the joystick port region ($c0-$ff) is being accessed. May be active-low logic and thus equivalent to KBSEL.|
|JyDs||I||Joystick 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.|
|M0-7||O||Not memory $0000-$7fff. 0 when the address is in this range, 1 otherwise.|
|M8-B||O||Not memory $8000-$bfff. 0 when the address is in this range, 1 otherwise.|
|MC-F||O||Not memory $c000-$ffff. 0 when the address is in this range, 1 otherwise.|
|CSCN4||I||Not 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.|
|CSRAM||I||Not 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.|
|CONT||I||A general-purpose input bit that can be read from port $dd, in later hardware it instead represents the Reset button state.|
|RAS0||O||These are all related to DRAM refreshing, and are used for the on-cartridge RAM in BASIC cartridges.|
|+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.|
|GG||I||Set to 0 for Game Gear mode, 1 for SMS mode.|
|TV||I||Set to 0 to remap the cartridge port for digital video input from the TV Tuner device. Set to 1 for regular usage.|
|TV L||I||Analogue audio inputs for the TV Tuner device.|
Connections needed for a convertor
You need to connect these lines as a bare minimum:
- M0-7 (connect to A15 if unavailable)
- 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:
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 pin||Slot pin|
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 pin||Slot pin|
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 pin||Slot pin|
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:
You can download all of the pinout diagrams in one PNG file, with no colour reduction (330KB).
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.
Go and edit from S8Dev:Pinouts-Index.