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= Registers =
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A register is a group of [[Flip-flop]]s.
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* Each flip flop shares a common clock
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* Each flip flop is capable of storing 1bit of info
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In general _a n-bit register is a group of n-flip-flops_
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Registers with combinational gates hold binary info, and the gates can
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determine how info is moved in/out of the register.
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== 4 bit register ==
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* Group of 4 [[D-flip-flop]]
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* Change on CLK positive edge
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* Has a clear_b signal that sets all registers to zero before the clock
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operates
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How to change only some bits?
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* All gates need to change in parallel
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* Sync the registers by directing control via the D-inputs of the flip flops
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* Add a load line, which can toggle if output of flip flop feeds back into D
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- By doing this we can keep the state of the flip flop
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== 4 bit shift register ==
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* Register that can shift the binary info held in each cell to its neighbor in
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a selected direction
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* Implementation
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- Cascade of flip flops
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- Output of a flip flop is connected to the D-input of the flip-flop at its
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right
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- Each clock pulse shifts the contents of the register on the bit position to
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its rights
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- The serial inputs determins the input into the left most flip-flop
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