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 (see #00500) Return: CF set on error AH = FFh error enabling address line 20 CF clear if successful AH = 00h in protected mode at specified address BP may be destroyed; all segment registers change Notes: BL and BH must be multiples of 8 the protected-mode CS must reference the same memory as the CS this function is called from because execution continues with the address following the interrupt call SeeAlso: AH=87h,AH=88h,INT 67/AX=DE0Ch Format of BIOS(Basic Input/Output System) A set of standardized calls giving low-level access to the hardware. The BIOS is the lowest software layer above the actual hardware and serves to insulate programs (and operating systems) which use it from the details of accessing the hardware directly. switch-to-protected-mode Global Descriptor Table: Offset Size Description (Table 00500) 00h 8 BYTEs null descriptor (initialize to zeros) 08h 8 BYTEs GDT descriptor (see #00501) 10h 8 BYTEs IDTsee Interrupt Descriptor Table descriptor 18h 8 BYTEs DS descriptor 20h 8 BYTEs ES 28h 8 BYTEs SS 30h 8 BYTEs CS 38h 8 BYTEs uninitialized, used to build descriptor for BIOS(Basic Input/Output System) A set of standardized calls giving low-level access to the hardware. The BIOS is the lowest software layer above the actual hardware and serves to insulate programs (and operating systems) which use it from the details of accessing the hardware directly. CS Format of segment descriptor table entry: Offset Size Description (Table 00501) 00h WORD segment limit, low word 02h 3 BYTEs segment base address, low 24 bits 05h BYTE access mode (see #00502) 06h BYTE 386+ extended access mode (see #00505) 07h BYTE 386+ segment base address, high 8 bits SeeAlso: #00500,INT 2C/AX=0002h,INT 31/AX=0009h Bitfields for segment descriptor table access mode field: Bit(s) Description (Table 00502) 3-0 segment type (see #00503,#00504) 4 descriptor type (1 = application, 0 = system) 6-5 descriptor privilege level 7 segment is present in RAM(Random Access Memory) See also DRAM, SRAM. SeeAlso: #00501,#00505 (Table 00503) Values for system segment descriptor type: 0 reserved 1 available 16-bit TSS 2 LDT 3 busy 16-bit TSS 4 16-bit call gate 5 task gate 6 16-bit interrupt gate 7 16-bit trap gate 8 reserved 9 available 32-bit TSS 10 reserved 11 busy 32-bit TSS 12 32-bit call gate 13 reserved 14 32-bit interrupt gate 15 32-bit trap gate SeeAlso: #00502,#00504 Bitfields for application segment descriptor type: Bit(s) Description (Table 00504) 3 code/data 0 date 1 code ---data segments--- 2 expand down 1 writeable ---code segments--- 2 conforming 1 readable ------ 0 accessed SeeAlso: #00502,#00503 Bitfields for 386+ segment descriptor table extended access mode field: Bit(s) Description (Table 00505) 3-0 high 4 bits of segment limit 4 available 5 reserved (0) 6 default operation size (1 = 32 bits, 0 = 16 bits) 7 granularity (1 = 4K, 0 = byte) SeeAlso: #00501,#00502,#02557