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study/sabre/os/files/ProtectedMode/DPMI1.0Spec/api/2f1687.html

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+<h2>Obtain Real-to-Protected Mode Switch Entry Point
+<img src="../0.9.gif" alt="[0.9]" width=22 height=17></h2>
+
+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. <p>
+
+<b>Call With</b><br>
+<img src="r/ax.gif" alt="" width=245 height=59><br>
+AX = 1687h <br clear>
+
+<b>Returns</b><br>
+<img src="r/ax+bx+cl+dh+dl+si+E+di.gif" alt="" width=245 height=59><br>
+<i>If function successful</i><br>
+AX = 0<br>
+BX = flags
+
+<blockquote><table border=1 cellspacing=0 cellpadding=4>
+<tr><th>Bit</th><th>Significance</th></tr>
+<tr><td rowspan=2 align=center>0</td><td align=left>0 = 32-bit programs are not supported</td></tr>
+<tr><td align=left>1 = 32-bit programs are supported</td></tr>
+<tr><td align=center>1-15</td><td align=left>not used</td></tr>
+</table></blockquote>
+
+CL = processor type
+
+<blockquote><table border=1 cellspacing=0 cellpadding=4>
+<tr><th>Value</th><th>Significance</th></tr>
+<tr><td align=center>02H</td><td align=left>80286</td></tr>
+<tr><td align=center>03H</td><td align=left>80386</td></tr>
+<tr><td align=center>04H</td><td align=left>80486</td></tr>
+<tr><td align=center>05H-FFH</td><td align=left>Reserved for future Intel processors</td></tr>
+</table></blockquote>
+
+DH = DPMI major version as a decimal number
+     (represented in binary)<br>
+DL = DPMI minor version as a decimal number
+     (represented in binary)<br>
+SI = number of paragraphs required for DPMI host
+     private data (may be 0)<br>
+ES:DI = segment:offset of procedure to call to enter
+        protected mode<p>
+
+<i>if function unsuccessful (no DPMI host present)</i><br>
+AX = nonzero<p>
+
+<h2>Notes</h2>
+
+<ul>
+
+<li>The entry point returned by <a href="2f1687.html">Int 2FH Function
+1687H</a> 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 <a href="../ch4.1.html">that page</a>.<p>
+
+<li>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).<p>
+
+</ul>
+
+