Franky, MSX cartridge

The Franky is a cartridge containing the audio- and video processor of the Sega Master System. The Sega seems to have a lot in common with the MSX. Both systems are based in the Z80 processor and the video processor of the Sega is quite similar to the first video processor of the MSX but with one special mode added. The memory mapping is comparable too, however most I/O addresses are different.

The extra mode of the video processor has very nice features, it is also a mode which works with ‘tiles’. This means the whole screen exists of patterns of 8*8 pixels, there is a table in the memory which describes which pattern to display at a specific position. Another table contains the patterns itself. A lot Sega games are taking advantage of this mode, so Franky makes these games playable on the MSX. The games must be patched because the I/O addresses are different compared to the original Sega system.

Carts are available at the Supersoniqs website.

The very first experiments, still using the MC1377 as the PAL encoder:

Final version:

The Franky uses a tripler for the clock of the video processor, this clock is retrieved by an analog circuit from the CPU clock of the MSX. This prevents interference with the video output of the MSX, for example when using two CRT monitors next to each other. One for the MSX output and one for this second video processor. A disadvantage is that the tripler is not compatible with MSXes running at 7MHz.

In fact all features are done by the Sega chip, two chips close to the slot are address decoders. The two 20 pins chips are an interfacing between the Sega chip and SRAM memory, originally the Sega was designed for older absolete memory chips.

The Sega chips do exist in two differen package types, both can fit on the PCB. The SDIP devices are usually the older version and seem to have a bug concerning the video output which affects the colours using the composite video output. This video processor doesn’t give horizontal sync pulses during the vertical blanking period, as a result no colour burts will be send as well and the colour decoder is not synchronised anymore.