diff --git a/ports/zephyr/bacport.h b/ports/zephyr/bacport.h
index 57ad6f39..d3dc88dc 100644
--- a/ports/zephyr/bacport.h
+++ b/ports/zephyr/bacport.h
@@ -29,7 +29,10 @@
 #include <zephyr/net/net_ip.h>
 #include <zephyr/net/socket.h>
 #include <zephyr/kernel.h>
-#include <bacnet/basic/object/device.h>
+/* BACnet Stack defines - first */
+#include "bacnet/bacdef.h"
+/* BACnet Stack API */
+#include "bacnet/basic/object/device.h"
 
 static inline char *inet_ntoa(struct in_addr in) {
     return "(inet_ntoa() to be implemented)";
diff --git a/ports/zephyr/rs485.h b/ports/zephyr/rs485.h
new file mode 100644
index 00000000..71bb27dd
--- /dev/null
+++ b/ports/zephyr/rs485.h
@@ -0,0 +1,89 @@
+/*####COPYRIGHTBEGIN####
+ -------------------------------------------
+ Copyright (C) 2004 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####*/
+
+#ifndef RS485_H
+#define RS485_H
+
+#include <stdint.h>
+/* BACnet Stack defines - first */
+#include "bacnet/bacdef.h"
+/* BACnet Stack API */
+#include "bacnet/datalink/mstp.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+    BACNET_STACK_EXPORT
+    void RS485_Set_Interface(
+        char *ifname);
+    BACNET_STACK_EXPORT
+    const char *RS485_Interface(
+        void);
+
+    BACNET_STACK_EXPORT
+    void RS485_Initialize(
+        void);
+
+    BACNET_STACK_EXPORT
+    void RS485_Send_Frame(
+        volatile struct mstp_port_struct_t *mstp_port,  /* port specific data */
+        uint8_t * buffer,       /* frame to send (up to 501 bytes of data) */
+        uint16_t nbytes);       /* number of bytes of data (up to 501) */
+
+    BACNET_STACK_EXPORT
+    void RS485_Check_UART_Data(
+        volatile struct mstp_port_struct_t *mstp_port); /* port specific data */
+    BACNET_STACK_EXPORT
+    uint32_t RS485_Get_Port_Baud_Rate(
+        volatile struct mstp_port_struct_t *mstp_port);
+    BACNET_STACK_EXPORT
+    uint32_t RS485_Get_Baud_Rate(
+        void);
+    BACNET_STACK_EXPORT
+    bool RS485_Set_Baud_Rate(
+        uint32_t baud);
+
+    BACNET_STACK_EXPORT
+    void RS485_Cleanup(
+        void);
+    BACNET_STACK_EXPORT
+    void RS485_Print_Ports(
+        void);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+#endif