HLASM: V1R6 Language Ref

Chapter 4. Machine instruction statementsThis chapter introduces a sample of the more common instruction formats andprovides general rules for coding them in their symbolic assembler languageformat.For the complete specifications of machine instructions, their object code format,their coding specifications, and their use of registers and virtual storage areas, seethe applicable Principles of Operation manual for your processor. If your programrequires vector facility instructions, see the applicable Vector Operations manual forthe complete specifications of vector-facility instructions.At assembly time, the assembler converts the symbolic assembler languagerepresentation of the machine instructions to the corresponding object code. Thecomputer processes this object code at execution time. Thus, the functionsdescribed in this section can be called execution-time functions.Also at assembly time, the assembler creates the object code of the data constantsand reserves storage for the areas you specify in your data definition assemblerinstructions, such as DC and DS (see Chapter 5, “Assembler instructionstatements”). At execution time, the machine instructions can refer to theseconstants and areas, but the constants themselves are not normally processed.As defined in the applicable Principles of Operation manual, there are five categoriesof machine instructions:v General instructionsv Decimal instructionsv Floating-Point instructionsv Control instructionsv Input/Output operationsEach is discussed in the following sections.GeneralinstructionsUse general instructions to manipulate data that resides in general registers or instorage, or that is introduced from the instruction stream. General instructionsinclude fixed-point, logical, and branching instructions. In addition, they includeunprivileged status-switching instructions. Some general instructions operate ondata that resides in the PSW or the TOD clock.The general instructions treat data as four types: signed binary integers, unsignedbinary integers, unstructured logical data, and decimal data. Data is treated asdecimal by the conversion, packing, and unpacking instructions.For further information, see “General Instructions” in the applicable Principles ofOperation manual.DecimalinstructionsUse the decimal instructions when you want to do arithmetic and editingoperations on data that has the binary equivalent of decimal representation.© Copyright IBM Corp. 1982, 2008 75