VTAM® provides a macroinstruction (the GENCB macroinstruction) that allows you to create control blocks and initialize certain fields during program execution. VTAM also provides macroinstructions (the MODCB, SHOWCB, and TESTCB macroinstructions) that allow you to test and change certain control block fields. In addition, macroinstructions are provided that generate DSECTs for the control blocks. These DSECTs enable control block fields to be located and tested with assembler language instructions. VTAM application program macroinstructions and control blocks are discussed in more detail in VTAM language.