I'm long time watching progress of VYMS cartridge for Commodore 128, Commodore 64 and Commodore VIC20 - video and audio extension with RS-232 port and 192K Video RAM
What it is:
Cartridge uses Yamaha V9958 VDP videochip (used in MSX2) - with higher resolution, more colors and more sprites than VIC-II or VIC-IIe has, VDC has still higher resolution and TED color count is much more lower.
Llook at features:
Video RAM: 128 KB + 64 KB of expanded VRAM Text modes: 80 x 24 and 32 x 24 Resolution: 512 x 212 (4 or 16 colors out of 512) and 256 x 212 (16, 256, 12499 or 19268 colors) Sprites: 32, 16 colors, max 8 per horizontal line Hardware acceleration for copy, line, fill, etc. Interlacing to double vertical resolution Horizontal and vertical scroll registers
VideoRAM used in VYMS cartridge offers 192K RAM, where is not comparagble even with our VDC
Cartridge uses also Yamaha YM2413 sound chip which offers 9 voices, 15 instrumentsThis is used also in MSX2 computer and was used also in music keyboards.
And there is also RS-232 serial port provided by 6551 ACIA and MAX-232 chips