Figure 1 shows the processor invocation argument list as it exists in the user's area. The 24-bit virtual addresses are passed in argument lists, control blocks, buffers, and user exit routines.

Entry and exit to the access method services processor occur through a module of the system adapter. Standard linkage is used; that is, register 1 points to the argument list, register 13 points to a save area, register 14 contains the return address, and register 15 contains the entry point address. On exit from the access method services processor, register 15 contains MAXCC. (See Processor Condition Codes.)

The argument list, as shown in Figure 1, can be a maximum of five fullword addresses pointing to strings of data. The last address in the list contains a 1 in the sign field. The first three possible strings of data begin with a 2-byte length field. A null element in the list can be indicated by either an address of zeros or a length of zero.