In Assembler language, linkage is performed according to the usual
   operating system (OS) conventions:

1. Register 1 points to the address list containing the parameter addresses. The high-order bit must be set in the last word. If no parameters are to be passed, Register 1 must contain the value 0 or must point to a fullword of value 0 with the high-order bit set.

2. Register 13 points to a register save area of at least 72 bytes (18 fullwords).

3. Register 14 points to the return point in the application program.

4. Immediately before a call to GDDM, Register 15 points to the entry point with the name "callname." On return from a call to GDDM, the top half of register 15 contains the error severity code; the bottom half contains the error number.

5. A branch to "callname" is performed.

Fullword integer

F-constant

Halfword integer

H-constant

Floating-point

E-constant

Character

C-constant

Array

Contiguous fullwords or halfwords

Structures

Use the appropriate storage mapping.

              CALL ASFCOL,(ID,COLOR),VL
              .........
     ID       DC   F'1'
     COLOR    DC   F'3'

     CALL FSINIT,(0),VL