Expansion bus slots
This page was last modified 01:32, 16 July 2019 by Gdx. Based on work by Mars2000you and Manuel and others.



Several expansion bus connectors exist on MSX. These type of connectors were especially prevalent on early MSX1 models. The MSX standard does not specify the shape or pin-out of these connectors. The most common type is the 50-pin IDC connector (standard 2.54mm pitch) with one or two polarizing key. Pins are generally more or less the same as a cartridge slot.

Very few, if any, devices exist to connect to most of these connectors. But they can often be modified to accept standard MSX cartridges. An example of such a conversion from Expansion bus to MSX Cartridge slot can be found here.

MSX models

that use a 50-pin IDC connector with one polarizing key

Expansion Bus with one polarizing key.jpg
50-Pin IDC.jpg

that use a 50-pin IDC connector with two polarizing keys

Expansion Bus with two polarizing keys.jpg

Pinout of the 50-pin IDC connector

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
Note: Pin used by the Frael Bruc 100 rev.1 for /SLTSL2 signal
Note: according to its service manual, Goldstar FC-200 has composite video signal on this pin
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 several MSXs.
  • SOUNDIN pin is not connected on several MSXs (Eg Toshiba HX-10DP).

Other expansion bus