Write this routine if you want to build a logon failure message (messages IKT00200I through IKT00204I) for a terminal that is not supported by TSO/VTAM. IKTCAS31 or IKTCASOY calls IKTCASX1 before TSO/VTAM sends the error message to the terminal. This gives the exit an opportunity to build its own message, including both text and device control characters, up to 160 characters. The message text must be located in the message buffer provided in Register 0 on entry.