diff --git a/mcp_can.cpp b/mcp_can.cpp
index 19a0822..375efe9 100644
--- a/mcp_can.cpp
+++ b/mcp_can.cpp
@@ -696,7 +696,7 @@ INT8U MCP_CAN::init_Filt(INT8U num, INT8U ext, INT32U ulData)
 ** Function name:           setMsg
 ** Descriptions:            set can message, such as dlc, id, dta[] and so on
 *********************************************************************************************************/
-INT8U MCP_CAN::setMsg(INT32U id, INT8U ext, INT8U len, INT8U rtr, INT8U *pData)
+INT8U MCP_CAN::setMsg(INT32U id, INT8U ext, INT8U len, INT8U rtr, const INT8U *pData)
 {
     int i = 0;
     m_nExtFlg = ext;
@@ -715,7 +715,7 @@ INT8U MCP_CAN::setMsg(INT32U id, INT8U ext, INT8U len, INT8U rtr, INT8U *pData)
 ** Function name:           setMsg
 ** Descriptions:            set can message, such as dlc, id, dta[] and so on
 *********************************************************************************************************/
-INT8U MCP_CAN::setMsg(INT32U id, INT8U ext, INT8U len, INT8U *pData)
+INT8U MCP_CAN::setMsg(INT32U id, INT8U ext, INT8U len, const INT8U *pData)
 {
     int i = 0;
     m_nExtFlg = ext;
@@ -784,7 +784,7 @@ INT8U MCP_CAN::sendMsg()
 ** Function name:           sendMsgBuf
 ** Descriptions:            send buf
 *********************************************************************************************************/
-INT8U MCP_CAN::sendMsgBuf(INT32U id, INT8U ext, INT8U rtr, INT8U len, INT8U *buf)
+INT8U MCP_CAN::sendMsgBuf(INT32U id, INT8U ext, INT8U rtr, INT8U len, const INT8U *buf)
 {
     setMsg(id, ext, len, rtr, buf);
     return sendMsg();
@@ -794,7 +794,7 @@ INT8U MCP_CAN::sendMsgBuf(INT32U id, INT8U ext, INT8U rtr, INT8U len, INT8U *buf
 ** Function name:           sendMsgBuf
 ** Descriptions:            send buf
 *********************************************************************************************************/
-INT8U MCP_CAN::sendMsgBuf(INT32U id, INT8U ext, INT8U len, INT8U *buf)
+INT8U MCP_CAN::sendMsgBuf(INT32U id, INT8U ext, INT8U len, const INT8U *buf)
 {
     setMsg(id, ext, len, buf);
     return sendMsg();
diff --git a/mcp_can.h b/mcp_can.h
index cbef86f..41479e0 100644
--- a/mcp_can.h
+++ b/mcp_can.h
@@ -89,8 +89,8 @@ private:
 *  can operator function
 */    
 
-    INT8U setMsg(INT32U id, INT8U ext, INT8U len, INT8U rtr, INT8U *pData); /* set message                  */  
-    INT8U setMsg(INT32U id, INT8U ext, INT8U len, INT8U *pData); /* set message                  */  
+    INT8U setMsg(INT32U id, INT8U ext, INT8U len, INT8U rtr, const INT8U *pData); /* set message                  */
+    INT8U setMsg(INT32U id, INT8U ext, INT8U len, const INT8U *pData); /* set message                  */
     INT8U clearMsg();                                               /* clear all message to zero    */
     INT8U readMsg();                                                /* read message                 */
     INT8U sendMsg();                                                /* send message                 */
@@ -100,8 +100,8 @@ public:
     INT8U begin(INT8U speedset);                                    /* init can                     */
     INT8U init_Mask(INT8U num, INT8U ext, INT32U ulData);           /* init Masks                   */
     INT8U init_Filt(INT8U num, INT8U ext, INT32U ulData);           /* init filters                 */
-    INT8U sendMsgBuf(INT32U id, INT8U ext, INT8U rtr, INT8U len, INT8U *buf);   /* send buf                     */
-    INT8U sendMsgBuf(INT32U id, INT8U ext, INT8U len, INT8U *buf);   /* send buf                     */
+    INT8U sendMsgBuf(INT32U id, INT8U ext, INT8U rtr, INT8U len, const INT8U *buf);   /* send buf                     */
+    INT8U sendMsgBuf(INT32U id, INT8U ext, INT8U len, const INT8U *buf);   /* send buf                     */
     INT8U readMsgBuf(INT8U *len, INT8U *buf);                       /* read buf                     */
     INT8U readMsgBufID(INT32U *ID, INT8U *len, INT8U *buf);         /* read buf with object ID      */
     INT8U checkReceive(void);                                       /* if something received        */