= Registers =

A register is a group of [[Flip-flop]]s.

* Each flip flop shares a common clock
* Each flip flop is capable of storing 1bit of info

In general _a n-bit register is a group of n-flip-flops_

Registers with combinational gates hold binary info, and the gates can
determine how info is moved in/out of the register.

== 4 bit register ==

* Group of 4 [[D-flip-flop]]
* Change on CLK positive edge
* Has a clear_b signal that sets all registers to zero before the clock
  operates

How to change only some bits?

* All gates need to change in parallel
* Sync the registers by directing control via the D-inputs of the flip flops
* Add a load line, which can toggle if output of flip flop feeds back into D 
  - By doing this we can keep the state of the flip flop

== 4 bit shift register ==

* Register that can shift the binary info held in each cell to its neighbor in
  a selected direction
* Implementation 
  - Cascade of flip flops
  - Output of a flip flop is connected to the D-input of the flip-flop at its
    right
  - Each clock pulse shifts the contents of the register on the bit position to
    its rights
  - The serial inputs determins the input into the left most flip-flop