Obtain Real-to-Protected Mode Switch Entry Point

This function can be called in real mode only to test for the presence of a DPMI host, and to obtain an address of a mode switch routine that can be called to begin execution in protected mode.

Call With

AX = 1687h
Returns

If function successful
AX = 0
BX = flags

Bit Significance

0 0 = 32-bit programs are not supported

1 = 32-bit programs are supported

1-15 not used

Bit	Significance
0	0 = 32-bit programs are not supported
1 = 32-bit programs are supported
1-15	not used

CL = processor type

Value Significance

02H 80286

03H 80386

04H 80486

05H-FFH Reserved for future Intel processors

Value	Significance
02H	80286
03H	80386
04H	80486
05H-FFH	Reserved for future Intel processors

DH = DPMI major version as a decimal number (represented in binary)
DL = DPMI minor version as a decimal number (represented in binary)
SI = number of paragraphs required for DPMI host private data (may be 0)
ES:DI = segment:offset of procedure to call to enter protected mode

if function unsuccessful (no DPMI host present)
AX = nonzero

Notes

The entry point returned by Int 2FH Function 1687H is only called for the first switch to protected mode by a DPMI client. For further details on the protocol for switching to protected mode and the environment after switching to protected mode, see that page.
Under DPMI hosts, the major version number is returned in DH and the minor version number is returned in DL. There are two decimal digits for the minor version number with the least-significant digit representing the revision number of the minor version number. Under DPMI version 0.9 hosts, DH is returned as 0, and DL is returned as decimal 90 (5AH). In hypothetical DPMI version 2.3, DH would be returned as 2 and DL would be returned as 30 (1EH).