Figure 8-5.—Illustrations of instruction word formats I, II, and III.addressing designator (i), a 3-bit base designator orare combined to define one of the following:special selection code (s), and a 13-bit address dis-operand, a constant that can be modified by an index, aplacement or operand designator (y). The b code (219jump address, an indirect address, or a string ofthrough 217) is used to identify the index register (0-7)identifier bits.being used for indexing or operand addressFormatsIV-AandIV-B—The formats are formodification. The i code (216) is a ZERO when in16-bit or half-word instructions. These instructionsdirect addressing mode and a ONE when in indirectreside in the upper or lower half-word of a memoryaddressing mode. The s and y codes (215 through 20)location. They are normally stored two to a memory8-9
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