14 Registers

Registers¶

binary storage device consisting of group of flipflops

• each flipflop in a register can store 1 bit binary
• for \(n\) bits, we need \(n\) flipflops

the frequency of the clocks are what determine the speed

this is what we talk about in ‘over-clocking’

4 bit register using D-FF¶

Register w/ \(\parallel\) load control¶

Load = 0¶

\(Q\) is fed back to the D FF

@ every clock pulse, output is re-written

Load = 1¶

sets/overwrites the previous value with new inputted value

Shift Register¶

a register capable of shifting binary information from 1 flip flop to another

Input and output can be serial/parallel

1. SISO
2. SIPO
3. PISO
4. PIPO

Shift-Right¶

Other Types¶

Bidirectional Shift¶

Rotate Shift¶

Right¶

Left¶

Universal Shift Register¶

contains

• features
  • clock pulse
  • reset/clear
  • four 4 x 1 mux for modes
  • No change
  • Shift Left
  • Shift Right
  • Parallel load
  • four d flipflops
• inputs
  • serial input for shift-left
  • serial input for shift-right

Ring/Shift-Register Counter¶

• circular shift-register
• mod(n) counter

in addition to regular SISO register

• the last FF output will be the first FF input
• only one FF is set (value = 1) at a time
• all others are cleared (value = 0)

if \(n =\) no of flipflops

• the no of distinguished states = mod(ring counter) = \(n\)
• to achieve a cycle, input is required \(n\) times

flowchart LR
1000 --> 0100 --> 0010 --> 0001 --> 1000

Ring Counter using decoder¶

1. one 2 bit counter
2. one \(2 \times 4\) decoder
3. four AND gates

Johnson Counter¶

other names

• Twisted Ring counter
• Switched Ring Tail counter
• mod(2n) counter

same as ring counter, but

• first i/p \(= Q'_0\)
• any no of 0s/1s is possible

if \(n =\) no of flipflops,

- no of states = \(2n\)¶

flowchart LR
0000 --> 1000 --> 1100 --> 1110 -->
1111 --> 0111 --> 0011 --> 0001 --> 0000

Diagrams¶

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