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Store (ST) and move (MOVE) instructions are, to a degree, synonymous. We use STORE when the source argument is a register and the destination is memory. Thus, |
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ST A, R1 |
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places the contents of (general register) R1 in memory location A, and |
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ST.F A, R1 |
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places the contents of floating register R1 in memory location A. |
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We use the MOVE construct in a more general way. Usually, MOVE implies that both source and destination operands are in memory, or both are in registers. Thus, |
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MOVE A, B |
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would replace (the word at memory location) A with (the word at memory location) B. Commonly, MOVE is used for strings of characters or decimal numbers. Thus, |
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MOVE.C A, B |
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moves the character string starting at memory location B to A. There is usually a length component associated with A and B, so that we probably should indicate |
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MOVE.C (l1,l2) A, B, |
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where l1 and l2 are the byte lengths of A and B, respectively. For purposes of this text, we frequently do not need to make these specifications, so that in MOVE.C A, B, the lengths of A and B are assumed to be defined earlier and known. |
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There is a special type of move associated with decimal arithmetic, called ZMOVE: |
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ZMOVE.P A, B. |
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This decimal move (packed format) operation requires that l1³ l2 and that all leading digits of l1 (the destination, or A in the above) be zeroed out. For strings, MOVE.C and ZMOVE.P are the two most frequently encountered operations. |
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MOVE can have a role for all register operands moving a value from one register to another, so that |
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MOVE.F R1, R2 |
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has the same effect as moving the value in floating-point register R2 to R1. |
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