BI-M DIRECTIONAL SHIFT REGISTERS

sometimes, the same shift register can be used as left shift or right shift with some additional circuits. we can multiply a binary number by 2 just simply placing the binary number in a shift register and shifting the number by one bit to the left. only care has to be taken that a ‘1’ is not shifted out of the most significant stage of the register. similarly, a binary number can be divided by ‘2’ when we simply shift the number to the right by one stage or one bit. the operation of bidirectional shift register can be explained using fig. 8.9. the bidirectional shift register is one in which the data can be shift either left or right. a three-bit bidirectional shift register using D flip-flop is shown in fig. 8.9 hare a set of NAND gets are used to select data input Frome the right or left adjacent flip-flop, as selected by the LEFT/RIGHT control line. the serial left shift and right shift operating and register can be performed by using LEFT/RIGHT control signal when the mode control signal LEFT/RIGHT=1 the data will be shift to the right when clock pulses are applied. in the mode control signal LEFT/RIGHT=0, the input data will be shifted to the left when clock pulses are applied. the mode control signal LEFT/RIGHT should be changed only when CLK=0, otherwise the data stored in the shift register may be changed.