AX = 0306H
Carry flag = clear (this function always succeeds)
BX:CX = real-to-protected mode switch address
SI:(E)DI = protected-to-real mode switch address
AX = new DS
CX = new ES
DX = new SS
(E)BX = new (E)SP
SI = new CS
(E)DI = new (E)IP
The processor is placed into the desired mode, and the DS, ES, SS, (E)SP, CS, and (E)IP registers are updated with the specified values; in other words, execution of the client continues in the requested mode at the address provided in registers SI:(E)DI. The values specified to be placed into the segment registers must be appropriate for the destination mode; if invalid selectors are supplied when switching into protected mode, an exception will occur.
The values in (E)AX, (E)BX, (E)CX, (E)DX, (E)SI, and (E)DI after the mode switch are undefined. (E)BP will be preserved across the mode switch call so it can be used as a pointer. On an 80386 or later CPU, the FS and GS segment registers will contain zero after the mode switch.
If interrupts are disabled when the mode switch procedure is invoked, they will not be re-enabled by the DPMI host (even temporarily).