Return Codes from MSGDISP

When the system returns control to the problem program, the low-order byte of register 15 contains a return code. The low-order byte of register 0 can contain a reason code. These codes are described in the following table:

Return Code	Reason Code	Meaning
0 (X'00')		Successful completion.
4 (X'04')		Device does not support MSGDISP.
8 (X'08')	1 (X'01')	Invalid input parameter.
	2 (X'02')	Invalid DCB or DEBCHK error.
	3 (X'03'	Environmental error.
	4 (X'04')	Authorization (TESTAUTH) violation.
	5 (X'05')	Invalid UCB. Requires the address of a UCB, not a UCB copy.
	6 (X'06')	Invalid request.
	11 (X'0B')	Unsuccessful ESTAE macro call.
	12 (X'0C')	Unsuccessful GETMAIN request.
12 (X'0C')		I/O error (The system posted the request for an error).

An I/O error occurs for load display if the drive display has a hardware failure.

If you get return code X'04' or X'0C' on a RESET UCBL operation, when you regain control, register 1 points to the UCB associated with the error.