diff --git a/bacnet-stack/npdu.c b/bacnet-stack/npdu.c
new file mode 100644
index 00000000..f327728f
--- /dev/null
+++ b/bacnet-stack/npdu.c
@@ -0,0 +1,121 @@
+/*####COPYRIGHTBEGIN####
+ -------------------------------------------
+ Copyright (C) 2005 Steve Karg
+
+ This program is free software; you can redistribute it and/or
+ modify it under the terms of the GNU General Public License
+ as published by the Free Software Foundation; either version 2
+ of the License, or (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to:
+ The Free Software Foundation, Inc.
+ 59 Temple Place - Suite 330
+ Boston, MA  02111-1307, USA.
+
+ As a special exception, if other files instantiate templates or
+ use macros or inline functions from this file, or you compile
+ this file and link it with other works to produce a work based
+ on this file, this file does not by itself cause the resulting
+ work to be covered by the GNU General Public License. However
+ the source code for this file must still be made available in
+ accordance with section (3) of the GNU General Public License.
+
+ This exception does not invalidate any other reasons why a work
+ based on this file might be covered by the GNU General Public
+ License.
+ -------------------------------------------
+####COPYRIGHTEND####*/
+#include <stdbool.h>
+#include <stdint.h>
+#include <assert.h>
+#include "bacdef.h"
+#include "bacenum.h"
+
+/* max-segments-accepted
+   B'000'      Unspecified number of segments accepted.
+   B'001'      2 segments accepted.
+   B'010'      4 segments accepted.
+   B'011'      8 segments accepted.
+   B'100'      16 segments accepted.
+   B'101'      32 segments accepted.
+   B'110'      64 segments accepted.
+   B'111'      Greater than 64 segments accepted.
+*/
+
+/* max-APDU-length-accepted
+   B'0000'  Up to MinimumMessageSize (50 octets)
+   B'0001'  Up to 128 octets
+   B'0010'  Up to 206 octets (fits in a LonTalk frame)
+   B'0011'  Up to 480 octets (fits in an ARCNET frame)
+   B'0100'  Up to 1024 octets
+   B'0101'  Up to 1476 octets (fits in an ISO 8802-3 frame)
+   B'0110'  reserved by ASHRAE
+   B'0111'  reserved by ASHRAE
+   B'1000'  reserved by ASHRAE
+   B'1001'  reserved by ASHRAE
+   B'1010'  reserved by ASHRAE
+   B'1011'  reserved by ASHRAE
+   B'1100'  reserved by ASHRAE
+   B'1101'  reserved by ASHRAE
+   B'1110'  reserved by ASHRAE
+   B'1111'  reserved by ASHRAE
+*/
+uint8_t npdu_encode_max_seg_max_apdu(int max_segs, int max_apdu)
+{
+    uint8_t octet = 0;
+
+    if (max_segs < 2)
+        octet = 0;
+    else if (max_segs < 4)
+        octet = 0x10;
+    else if (max_segs < 8)
+        octet = 0x20;
+    else if (max_segs < 16)
+        octet = 0x30;
+    else if (max_segs < 32)
+        octet = 0x40;
+    else if (max_segs < 64)
+        octet = 0x50;
+    else if (max_segs == 64)
+        octet = 0x60;
+    else
+        octet = 0x70;
+
+    // max_apdu must be 50 octets minimum
+    assert(max_apdu >= 50);
+    if (max_apdu == 50)
+        octet |= 0x00;
+    else if (max_apdu <= 128)
+        octet |= 0x01;
+    //fits in a LonTalk frame
+    else if (max_apdu <= 206)
+        octet |= 0x02;
+    //fits in an ARCNET or MS/TP frame
+    else if (max_apdu <= 480)
+        octet |= 0x03;
+    else if (max_apdu <= 1024)
+        octet |= 0x04;
+    // fits in an ISO 8802-3 frame
+    else if (max_apdu <= 1476)
+        octet |= 0x05;
+
+    return octet;
+}
+
+int npdu_encode(
+  uint8_t *buf,
+  BACNET_ADDRESS *dest,
+  BACNET_ADDRESS *src,
+  bool data_expecting_reply,
+  uint8_t invoke_id)
+{
+  int len = 0;
+
+  return len;
+}