HuC6270 - Video Display Controller (VDC).

(see ../images/220px-HuC6270A_01.jpg)

The specifications for the VDC (referred to as “7UP” by NEC-HE) are,

• 1 background layer made of 8x8 tiles.
• 64 simultaneous sprites.
• 64KB VRAM.
• 20 internal 16-bit registers.
• 2 16-bit IO ports.

The VDC can address up to 128K of VRAM.  But as it only has 64KB, the latter half of the 128KB mirrors the first 64KB.  Note that reading the mirror area may returns corrupted data, and writes through the IO ports or the DMAs to that area are always ignored.  The VDC can be accessed through 2 16-bit IO ports located in the hardware page ($ff).

• VDC I/O Ports and Registers
• VDC Functions