7.3 Machine Language 195 The register specifier is 0, which refers to the A register, and the addressing mode is immediate, meaning that the value to be loaded is in the operand specifier. That is, the data is in the operand specifier; thus it is shaded gray. After execution of this instruction, the contents of the second and third bytes of the instruction (the operand specifier) would be loaded into the A register (the accumulator). That is, the A register would contain 0007 and the original contents of A would be lost. To simplify the discussion, from here on we represent all numbers in hexadecimal (except the bit strings in the registers). We specify leading zeros on addresses but not on numeric values. Here is another load instruction. The register specifier is 1, which refers to the X register, and the addressing mode is immediate. Thus, the data to be loaded into the X register is stored in the operand specifier itself. After the execution of this instruction, the X register would contain 1F. Note that the original contents of the X
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This note was uploaded on 01/13/2011 for the course CSE 1550 taught by Professor Marianakant during the Fall '10 term at York University.