The on-board CMOS has a built-in 128 character ROM. The HDSP211XS also has a user definable character (UDC) feature, which uses a RAM that permits storage of 16 arbitrary characters, symbols or icons that are software-definable by the user. The character ROM itself is mask programmable and easily modified by the manufacturer to provide specified custom characters. The HDSP211XS is designed for standard microprocessor interface techniques, and is fully TTL compatible. The Clock I/O and Clock Select pins allow the user to cascade multiple display modules.