Q. Illustrate Left shift register with parallel load?

A register that shifts data in one direction only is known as Uni-directional shift register and a register that can shift data in both directions is known as bi-directional shift register. Shift register can be created for bi-directional shift with parallel input-output. A general shift register structure can have parallel data transfer to or from register along with added facility of right or left shift. This structure will need extra control lines for indicating whether serial or parallel output is desired and right or left shift is required. A general representative diagram is displayed in figure below for this register.

There are 3 major control lines displayed in above figure. If parallel load enable is active, parallel input-output operation is done or else serial input- output shift select line for selecting left or right shift. If it has value 0 then right shift is performed and for value 1 left shift is performed. Shift enable signal denotes when to start shift.

Figure: 4 - bit left shift register with parallel load