GENCB macroinstruction

GENCB builds and initializes an NIB, ACB, RPL, or EXLST. To use GENCB, this information is specified:

The kind of control block built: ACB, NIB, RPL, or EXLST.
The fields initialized and the values set in each field. For example, to build an RPL and initialize the OPTCD field to SYN, specify:
```
GENCB BLK=RPL,AM=VTAM,OPTCD=SYN
```
The number of copies of the control block built. Each copy initializes with the same values and can later modify with the onset of particular requests.
Where the control block is built. The program defines an area where VTAM® builds the control block. If an area is not specified, VTAM gets the storage from the system dynamically. VTAM returns the address of the created control block in register 1 and the length in register 0.

For application programs, any control block allocated using the GENCB macroinstruction resides in 24-bit storage.