VTAM Exit Services parameter list

When VTAM® Exit Services gets control, the address of the following parameter list must be in register 1.

Table 1. VTAM Exit Services parameter list
Dec (Hex) Offset	Size (Bytes)	Value when Calling VTAM Exit Services	Description
0 (0)	4	An address provided by VTAM	A pointer to a Supported Functions bitmap indicating which VTAM Exit Services functions are available.
4 (4)	1	X'01'	One-byte function code to indicate the requested function of VTAM Exit Services. (X'01' indicates the message function). Any other value will result in an error message on the system console and a non-zero return code being returned to the exit.
5 (5)	3	Reserved	Reserved
8 (8)	4	An address provided by VTAM	Address of the VTAM Exit Services module (ISTIECXS). ISTIECXS resides below the 16M line.
12 (C)	4	An address provided by the session management exit routine	List to be passed to VTAM Exit Services (pointer to the VTAM Exit Services Message parameter list)
16 (10)	4	Reserved	Reserved

The VTAM Exit Services parameter list contains a pointer to the Supported Functions bitmap which indicates which functions are supported by the current level of VTAM Exit Services. The exit should verify the requested function is supported before calling VTAM Exit Services. This bitmap allows an exit to be migrated to different levels of VTAM more easily. The structure of the Supported Functions bitmap is shown in Table 2:

Table 2. VTAM Exit Services supported functions bitmap
Byte	Description
0	Bit Setting: B'1... ....' This is the last fullword of the VTAM Exit Services Supported Functions bitmap. B'0... ....' There is at least one more fullword of the VTAM Exit Services Supported Functions bitmap following this fullword. The last fullword of the bitmap will have the high-order bit on. B'.1.. ....' The message function is available from VTAM Exit Services. B'.0.. ....' The message function is not available from VTAM Exit Services. All remaining bits are reserved.
1	Reserved
2	Reserved
3	Reserved