diff --git a/src/RS232.h b/src/RS232.h
--- a/src/RS232.h
+++ b/src/RS232.h
@@ -33,6 +33,7 @@ rs232extern int rs232close(rs232port_t f
 rs232extern int rs232setup(rs232port_t fd, int ChSize, int BaudeRate, rs232parity Parity, rs232stop NbStop);
 rs232extern int rs232write(rs232port_t fd,char *psWrite, int WriteBufferSize);
 rs232extern int rs232read(rs232port_t fd,char *psRead, int ReadBufferSize);
+rs232extern int rs232availablebytes(rs232port_t fd);
 rs232extern int rs232setparity(rs232port_t fd, rs232parity Parity);
 rs232extern int rs232setnbstop(rs232port_t fd, rs232stop NbStop);
 rs232extern int rs232setcsize(rs232port_t fd, int ChSize);
diff --git a/src/RS232_unix.c b/src/RS232_unix.c
--- a/src/RS232_unix.c
+++ b/src/RS232_unix.c
@@ -425,6 +425,12 @@ int rs232write(rs232port_t fd,char *psWr
     }
 }
 
+int rs232availablebytes(rs232port_t fd)
+{
+    int bytes;
+    ioctl(fd, FIONREAD, &bytes);
+    return bytes;
+}
 
 int rs232read(rs232port_t fd,char *psReadHex, int ReadBufferSize)
 {
diff --git a/src/RS232_win.c b/src/RS232_win.c
--- a/src/RS232_win.c
+++ b/src/RS232_win.c
@@ -322,6 +322,13 @@ int rs232read(rs232port_t fd,char *psRea
 
 }
 
+int rs232availablebytes(rs232port_t fd)
+{
+    DWORD dwErrorFlags;
+    COMSTAT ComStat;
+    ClearCommError(m_hIDComDev, &dwErrorFlags, &ComStat);
+    return((int)ComStat.cbInQue);
+}
 
 int rs232saferead(rs232port_t fd,char* data,int count )
 {