Today I received a Franky cartridge from Sander van Nunen after I offered to look into how things work with it. But first a few specifics...

Franky is a cartridge extension containing a 315-5124 chip, which is available in the Sega Master System consoles. This chip contains both a VDP and the SN76489 PSG. The VDP is based on the TMS9928A and extended with some console-specific features:

• palette in 2 banks with 16 colors each of which 1 bank dedicated to backdrop and sprite colors
• horizontal and vertical hardware scrolling
• TMS9928 style tile patterns and sprites where each pixel can have its own color
• line interrupt
• extended name table with up to 512 tiles, options to mirror, flip, change priority (sprites will go behind it) and palette bank for a tile
• flags to disable specific rows or columns from scrolling (useful for score boards in games that use scrolling)
• access to horizontal and vertical counters

The audio exits 2-way, to the MSX via de cartridge slot and via de 15-pin SUB-D (VGA connector), which has the same pinout as the ESE3 for convenience purposes.

Right now many Sega Master System titles can be played when they get converted while the game files get loaded. Some titles have been converted manually already as the automated converter has problems converting those.