Spectravideo SVI-811
This page was last modified 00:55, 18 January 2021 by Mars2000you. Based on work by NYYRIKKI and Rderooy and others.



The SVI-811 is a special MSX Game Adapter (Adaptor on the label and the box) to be installed in the IBM PC Compatible SVI-838 (aka X'press 16).

It consisted of

  • a full length ISA card with a Z80 processor (SVI-811A)
  • an external module (SVI-811B) that is attached to the ISA card with the MSX1 BIOS-BASIC rom, an MSX cartridge slot and MSX game ports.

On the front facing side of the SVI-811B adapter, there's a slider to select COMPUTER mode (PC) or GAME mode (MSX).

Although Spectravideo custom chips have not been used, it seems SVI-811 is mostly based on Spectravideo MSX design while SVI-838 is mostly based on Bondwell design.


  • On the systemboard of the SVI-838 there is the MSX2 V9938 video chip, but the SVI-811 BIOS allows to run only MSX1 games on cartridge.
  • MSX1-BASIC can't be used directly due to lack of keyboard support (and PPI)
  • Mouse doesn't work with the adapter due to port timing problems, caused by custom connection that skips PSG.
  • Cartridge slot does not have all standard signals.
  • No printer or cassette connectors
  • SVI-838 floppy drives can't be used.
Brand Spectravideo
Model SVI-811
Year 1986
Launch price
RAM 64kB (Shared resource with SVI-838)
VRAM 128kB (Shared resource with SVI-838)
Media MSX cartridges
Video V9938 with superimposition with the CGA VDP (Yamaha V6355) (Shared resource with SVI-838)
Audio AY-3-8912 PSG (Shared resource with SVI-838)
Keyboard layout FIN/SWE QWERTY (Not usable)
Extras superimposing feature
Emulation ROM dumped, mainly for archival purposes. It is unknown if this can be emulated.


Spectravideo SVI-811 package
Spectravideo SVI-811 module
Spectravideo SVI-811 module (front)
Spectravideo SVI-811 box
Spectravideo SVI-811 ISA card
SVI-811 ISA card (underside)
SVI-811 module left side
SVI-811 ISA card installed in SVI-838
SVI-811 module attached to SVI-838
Spectravideo SVI-811 module - cartridge slot
Soectravideo SVI-811 module with King's Valley II cartridge
Spectravideo SVI-811 label


The SVI-811, combined with the SVI-838 PC, is a MSX1 without MSX-Engine. The CPU is a Z80A from Zilog.

Slot Map

Slot 0 Slot 1 Slot 2 Slot 3
Page C000h~FFFFh 64kB RAM Cartridge
Page 8000h~BFFFh
Page 4000h~7FFFh Main-ROM
Page 0000h~3FFFh

Due to lack of PPI, slot (0-3) select signals are handled by IC19 (74LS139) pins 12-9 on SVI-811A.


Some of the cartridge slot signals are missing though. Some of these are required ie. by modern MegaROM games and memorycard readers, but luckily there are enough free pins to connect these on the edge connector between SVI-811A and SVI-811B.

The missing signals are /RFSH, /WAIT, /INT, /M1, /BUSDIR, CLOCK, +12V, SOUNDIN and -12V

Tips n' tricks

Due to fact that CGA graphics are superimposed over V9938 on the SVI-838, in order to play Japanese/USA games on original 60Hz frequency both V9938 and V6355 need to be changed to 60Hz mode.

60Hz pseudocode:
SVI-811: OUT #99,0:OUT #99,#89:OUT #B5,#65:OUT #B6,0
(SVI-838: OUT #3C1,#80:OUT #3C2,#89:OUT #3DD,#65:OUT #3DE,1)

50Hz pseudocode:
SVI-811: OUT #99,2:OUT #99,#89:OUT #B5,#65:OUT #B6,8
(SVI-838: OUT #3C1,#82:OUT #3C2,#89:OUT #3DD,#65:OUT #3DE,9)

How to upgrade to MSX2

NYYRIKKI has succeeded to update the SVI-811 to MSX2. However, the other limitations of the SVI-811 Adapter are still present, especially only games and applications in ROM format can be used and it's impossible to use keyboard or mouse. External floppy interface may work, but in order to use modern memory card interfaces such as Carnivore2 the missing CPU signals need to be connected to cartridge slot.

Minimum upgrade steps are:

  • using a Main-ROM with "No RTC" MSX2 BIOS and adding OUT &HB5,&H65:OUT&HB6,8 at the boot beginning to replace the MSX1 rom included in the SVI-811B
  • mounting a socket on back of the BIOS/BASIC rom for the MSX2 Sub-ROM
  • connecting /OE to cartridge slot /RD
  • routing /CE trough 50-pin connector (ie free pin 7) back to SVI-811A ISA card and connecting it there to IC19 (74LS139)

The slot 3 signal is free for Sub-ROM on pin 9 of IC19, but it is recommended to swap pin 9 and 11 wires in order to move RAM to slot 3 instead.