Advantech ADAM-5511 Manual page 276

Clear Local Loopback
Set Local Loopback
Set specified port to disable loopback function for diagnostic
Set specified port to enable loopback function for diagnostic
void port_clear_local_loopback(int portno)
void port_set_local_loopback(int portno)
portno
None
void main ()
{
port_install(1);
:
:
port_enable_fifo(1);
//set port1 to enable loopback function for diagnostic
port_set_local_loopback(1);
//or "port_clear_local_loopback(1)"
}
The specified port number