MSX Cartridge slot
This page was last modified 11:42, 20 February 2018 by Mars2000you. Based on work by Gdx and Rderooy and others.
MSX Cartridge Slot

The MSX cartridge slot is the standard expansion port, as defined in the MSX standard definition. It can be used for program cartridges, such as games, or for hardware expansion.

Most MSX systems have two primary slots available for expansion, although some have just one, and may have a proprietary expansion slot.

A primary expansion slot can be split into 4 sub-slots using a Slot Expander.


Standard MSX Cartridge slot

MSX Cartridge slot pinout.jpg
Pin Name Type Description
1 /CS1 O ROM addresses 4000-7FFF select signal
2 /CS2 O ROM addresses 8000-BFFF select signal
3 /CS12 O ROM addresses 4000-BFFF select signal (for 256k ROM)
4 /SLTSL O Slot select signal
5 RSV (N.C) Reserved signal line - use inhibited
6 /RFSH O Refresh cycle signal
7 /WAIT I CPU's WAIT request signal
8 /INT I Interrupt request signal to CPU
9 /M1 O Signal expressing CPU fetch cycle
10 /BUSDIR I This signal controls direction of external databus buffer Cartridges are selected and L level is output from each cartridge at data transmission time
11 /IORQ O I/O request signal
12 /MERQ O Memory request signal
13 /WR O Write timing signal
14 /RD O Read timing signal
15 /RESET O System reset signal
16 RSV(N.C) Reserved signal line - use inhibited
17 A9 O Address bus signals
18 A15 O Address bus signals
19 A11 O Address bus signals
20 A10 O Address bus signals
21 A7 O Address bus signals
22 A6 O Address bus signals
23 A12 O Address bus signals
24 A8 O Address bus signals
25 A14 O Address bus signals
26 A13 O Address bus signals
27 A1 O Address bus signals
28 A0 O Address bus signals
29 A3 O Address bus signals
30 A2 O Address bus signals
31 A5 O Address bus signals
32 A4 O Address bus signals
33 D1 I/O Data bus signals
34 D0 I/O Data bus signals
35 D3 I/O Data bus signals
36 D2 I/O Data bus signals
37 D5 I/O Data bus signals
38 D4 I/O Data bus signals
39 D7 I/O Data bus signals
40 D6 I/O Data bus signals
41 GND PWR Signal ground
42 CLOCK O CPU clock 3.579545MHz
43 GND PWR Signal ground
44 SW1 For insertion/removal protect
45 +5V PWR +5V power source
46 SW2 For insertion/removal protect
47 +5V PWR +5V power source
48 +12V PWR +12V power source
49 SOUNDIN I Sound input signal (-5bdm)
50 -12V PWR -12V power source


  • Signals are TTL compatible.
  • Power source +5V must be 300mA max per slot.
  • Power source -/+12V must be 50mA max for all slots. Not connected on MSXs Casio, Yamaha SX-100 and Hitachi MB-H1.


These signal diagrams indicate the maximum timings for a proper operation.

Cycle M1

primary slot
secondary slot

Memory cycle

primary slot
secondary slot

I/O cycle

primary slot
secondary slot

Fan-IN/OUT on data address bus

Fan-in/out is a term that defines the maximum number of digital inputs/outputs that a single logic gate can accept.




Slot depth


MSX Cartridge Case Dimensions

  • STL files for 3D printing your own cartridges.

Machines without MSX cartridge slot

However, a proprietary expansion bus is present on the Daewoo CPC-88 and version 1 of the Frael Bruc 100.

Machines with only 1 MSX cartridge slot

Many MSX1 machines and a few MSX2 machines have only 1 MSX cartridge slot, but most of them have a proprietary expansion bus which can be used as second cartridge slot. Besides, a module slot can be present when it's a computer manufactured by Yamaha.

The following machines with only 1 MSX cartridge slot don't have an expansion bus (or a Yamaha module slot), so the only solution is to insert a slot expander in the unique MSX cartridge slot:

Machines with more than 2 MSX cartridge slots

There are also machines with 2 cartridge slots and an expansion bus (or Yamaha module) slot: