IBM System/7 Functional Characteristics - All about the IBM 1130 ...

' rrrI !Mil,. '11111E1 luluINSTRUCTION FORMATSTwo instruction formats are used in the System/7 processor: a 16-bit short-formatinstruction (one word) and a 32-bit long-format instruction (two words), as shown inFigure 4-2.Both instruction formats are divided into several fields whose contents specify theoperation to be performed and the location of the data to be processed. Most format fieldshave the same meaning from one instruction to the next; some, however, have specialmeanings, depending on the particular instruction. These exceptions are discussed in thedetailed description of the instruction.The operation-code (Op code) field is five bits in length and specifies the instructionto be performed.The register (R) field is three bits in length and indicates whether the accumulator,instruction address register, or one of the index registers is to take part in the instructionexecution. An R field of 000 specifies either the accumulator or the instruction addressregister (IAR), depending on the instruction. The index registers are specified by thefollowing R fields:001 — index register 1010 — index register 2011 — index register 3100 — index register 4101 — index register 5110 — index register 6111 — index' register 7The contents of the R field register are used for (1) generating an effective address tolocate the operand, (2) as an instruction operand, or (3) as data sent to or received froman I/O device.Short formatBit0 4 5 7 8 15Field nameOp codeI I I 1Register(13)I IDisplacement111(11iFirst hex Fourth hexcharacter characterOne wordLong formatBitField name0 4 5 7 8 1516Op codeI 1 IFirst hexcharacterRegister(A)_ IDisplacement1 1 I 1 1 1 I 1 1 131Address1 1 1 1 1 1 1 1 1 1 1 1Eighth hexcharacterFirst word Second wordFigure 4-2. Instruction formatsProcessor Instructions 4-5