INT 15 - SYSTEM - SWITCH TO PROTECTED MODE
AH = 89h
BL = interrupt number of IRQ0 (IRQ1-7 use next 7 interrupts)
BH = interrupt number of IRQ8 (IRQ9-F use next 7 interrupts)
ES:SI -> GDT for protected mode
offset 0h  null descriptor (initialize to zeros)
8h  GDT descriptor
10h  IDT descriptor
18h  DS
20h  ES
28h  SS
30h  CS
38h  uninitialized, used to build descriptor for BIOS CS
CX = offset into protected-mode CS to jump to
Return: CF set on error
AH = FFh  error enabling address line 20
CF clear if successful
AH = 00h
in protected mode at specified address
Note:   BL and BH must be multiples of 8
SeeAlso: AH=88h,INT 67/AX=DE0Ch

See also: 1587

1589 - SYSTEM - SWITCH TO PROTECTED MODE