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Unformatted text preview: 32,767 to +32,767 in decimal. This information is important when working with the Pep/7 machine. The number of bits we have available determines the size of the numbers we can work with. Instruction Format We have talked about instructions going into the instruction register, being decoded, and being executed. Now we are ready to look at a set (or subset) of concrete instructions that a computer can execute. But first, we need to examine the format of an instruction in Pep/7. Figure 7.2 shows the format for an instruction in Pep/7. There are two parts to an instruction: the 8-bit instruction specifier and (optionally) the 16-bit operand specifier . The instruction specifier (the first byte of the instruction) indicates what operation is to be carried out, such as Add a number to a value already stored in a register, and how to interpret just where the operand is. The operand specifier (the second and third bytes of...
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- Fall '10