Shift rnicrooperations are used for serial transfer of data. They are also used in conjunction with arithmetic, logic, and other data-processing operations. The contents of a register can be shifted to the left or the right. At the same time that the bits are shifted, the first flip-flop receives its binary information from the serial input. During a shift-left operation the serial input transfers a bit into the rightmost position. During a shift-right operation the serial input transfers a bit into the leftmost position. The information transferred through the serial input determines the type of shift. There are three types of shifts: logical, circular, and arithmetic.
A logical shift is one that transfers 0 through the serial input. We will adopt the symbols shl and shr for logical shift-left and shift-right rnicrooperations. For example:
R1 +- shl R1
R2 +-shr R2
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are two rnicrooperations that specify a 1-bit shift to the left of the content of register R 1 and a 1-bit shift to the right of the content of register R2. The register symbol must be the same on both sides of the arrow. The bit transferred to the end position through the serial input is assumed to be 0 during a logical shift.