Underline location     index 14h  CRTC

Layout  b6     DW   Double word mode
        b5     CB4  Count by 4
        b4-b0  UL   Underline location

- Double word mode (bit 6)
        0 : Normal word addressing.
        1 : Double word addressing (mode 13h chained).

- Count by four (bit 5)
        0 : Normal clocking
        1 : Divide the character clock to the memory address counter
            by 4 (mode 13h chained).

- Underline location (bits 4-0)
        The value in this field minus one determines the horizontal
        scan line within a character box on which the underline will
        occur (text modes).