The D’s are the parallel inputs and the Q’s are the parallel outputs. The following circuit is a four-bit parallel in – parallel out shift register constructed by D flip-flops. Parallel In – Parallel Out Shift Registersįor parallel in – parallel out shift registers, all data bits appear on the parallel outputs immediately following the simultaneous entry of the data bits. VHDL Code for shift register can be categorised in serial in serial out shift register, serial in parallel out shift register, parallel in parallel out shift register and parallel in serial out shift register. VHDL Code for Serial In Parallel Out Shift Register.Serial In – Parallel Out Shift Registers.VHDL code for Parallel In Parallel Out Shift Register.Parallel In – Parallel Out Shift Registers.