Yamaha Expansion Bus Connector
This page was last modified 09:14, 21 May 2022 by Gdx. Based on work by Mars2000you and Rderooy.


Early MSX1 models manufactured by Yamaha have only one cartridge slot, but they come with a special expansion bus. With the use of the Yamaha CA-01 adapter a regular MSX cartridge can be plugged into the rear expansion bus slot.

The Expansion port is actually a male edge connector. By default it is covered up to prevent dirt from entering the system, or accidental shorting of pins.

The MSX2 YIS-805/128 and YIS-805/256 also have an expansion bus, but these machines already have two MSX catridge slots, and the expansion bus is probably different, as it is meant for a digitizer.


The pinout is same as the cartridge slot connector that just has been carried over to a male edge connector.

Yamaha BUS.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 (N.C.) For insertion/removal protect
45 +5V PWR +5V power source
46 SW2 (N.C.) 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.
  • Power source -/+12V must be 50mA max for all slots.

Systems with the Yamaha expansion bus connector

Model Generation Remark
Sakhr AX-100 MSX1 Can't be used as it is occupied by Arabic rom
Victor HC-5 MSX1
Victor HC-6 MSX1
Victor HC-60 MSX1
Yamaha CX5 MSX1
Yamaha CX5F MSX1
Yamaha CX5M MSX1
Yamaha YIS-303 MSX1 Not easy to use as access is blocked
Yamaha YIS-503 MSX1
Yamaha YIS-503F MSX1
Yamaha YIS-805/128 MSX2 Reserved for a digitizer, also known as 'video enhancer'
Yamaha YIS-805/256 MSX2 Reserved for a digitizer, also known as 'video enhancer'