315-5750
From MegaDrive Wiki
The 315-5750 chip was an expansion chip designed by Sega to render polygons in real-time. It can calculate between 300 and 600 polygons per frame, running internally at 15 frames per second.
Internally, the chip is thought to be a Sega-branded Samsung SSP1601 16-bit Fixed Point DSP. The chip connects to both a 128 KByte (64KWord x 16 bit) DRAM to hold rendered tiles from which the Mega Drive does a DMA transfer from, as well as the 2 MByte mask ROM that holds the actual game.