Serial Inteface w/ builtin CSU/DSU question

[Raul Fernandez]

Dear Group,   Are there any built in test in CISCO routers with built in CSU/DSU that will let you test the CSU/DSU? I know about loop back test ect and debuging the serial interface itself but I am looking for commands that test the internal CSU/DUS specifically. Thank you for time.   Sincerely,   Raul