28? How very interesting!
Slightly higher resolution, it appears (256x210), and 16 full colors from a 512 color palette, plus 80-column text, high resolution (512x192) and hardware scroll. Plus still more... how very cool.
It does appear very similar to Sega's chip. This would have been a fantastic chip to have, it has all the features I was wishing for.
The datasheet is all over the net... there's a note in an old TI newsletter that the 9938 was derived from the 9928 (but was not compatible), many of the otehr hits are in Japanese.
Interesting.. it would have been nice to have had this chip!