The mfpubcas.cpy copybook contains several 78-level fields you can use to call API functions. These are documented in the copybook itself, under a section labeled functions. The name of each field describes the function itself.
The following is a partial listing from mfpubcas.cpy:
...
      *=================================================================
      *    functions
      *=================================================================
           03  ()-FUNC                       PIC X(4).
                78  78-CAS-FUNC-OPEN         VALUE 'OP  '.
                78  78-CAS-FUNC-OPIO         VALUE 'OPIO'.
                78  78-CAS-FUNC-CLOS         VALUE 'CLOS '.
                78  78-CAS-FUNC-GN           VALUE 'GN  '.
... 
            	 move 78-CAS-FUNC-GN to WS-FUNC
A typical sequence of calls would contain the following functions:
| Function | Purpose | 
|---|---|
| 78-CAS-FUNC-OPEN | To open the file | 
| 78-CAS-FUNC-STGT | To position on a particular record (e.g., start, key greater than, etc.) | 
| 78-CAS-FUNC-GN | To get the next record, and then repeated to get each subsequent record until all required records have been returned | 
| 78-CAS-FUNC-CLOS | To close the file |