Using save-area module linkage conventions

Figure 1 shows the save-area module linkage convention for APPN used by some VTAM® modules. To determine the convention used for your module, find the location pointed to by register 13 and check the 8-byte field preceding this address. If you find an 8-byte module name such as ISTACCRT, your module was coded using the save-area module linkage convention for APPN. The first three characters will always be IST for a VTAM module.

The addresses of the module work areas for modules using the save-area module linkage convention for APPN are stored in process scheduling services (PSS) control blocks. The first word of the save-area, pointed to by register 13, contains the pointer to the VTAM work area (VWA) header in the PSS.

For the save-area module linkage convention for APPN, the following save-area format pointed to by the address in register 13 is used:

Offset: Contents
X'-08': Module eye-catcher C'XXXXXXXX'
X'+00': Address of ISTVWA
X'+04': Backward save-area pointer (to previous save-area)
X'+08': Pointer to next available area
X'+0C'...: Registers 14 - 12

Figure 1. Save-area module linkage conventions—APPN

Diagram that shows data areas used by channel programs for PU types 2 and 4.