AH = 14h
        AL = 0 load user-specified font
            ES:DI = pointer to character font
            BH = number of bytes per character
            BL = 0: load main font (block 0)
                 1: load alternate font (block 1)
            CX = number of characters to store
            DX = character offset into RAM font area
        AL = 1 load system rom default font
            BL = 0: load main font (block 0)
                 1: load alternate font (block 1)
        AL = 2 set mapping of LCD high intensity attributes
            BL = 0: ignore high intensity attribute
                 1: map high intensity to underscore
                 2: map high intensity to revrese video
                 3: map high intensity to selected alternate font
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