WANTED: Individual or team to take over this project. I'm in my 70's and want to put my feet up. Contact details in footer.

  A Level    Sequential Logic    Questions 0 to 4   -->  View All  

The Shift Register

• On the rising edge of the clock pulse, each D is copied to the next Q and all the data moves one place to the right.
• The data moves one place to the right along the shift register like suitcases on a conveyor belt.
• Pulses can be delayed using this circuit.
• Shift registers can be used in simple combination locks. The registers have to be clocked in the correct sequence to unlock the door.

SIMULATION

Pseudo-Random Number Generator

SIMULATION

Notice the diagonal pattern in the truth table.

Each row is copied and shifted one place to the right.
All shift registers work like this.

Serial In, Parallel Out, SIPO

The shift register can be used to delay pulses.

It can also be used to collect a serial stream of pulses. Once all the bits (usually eight) have been collected (a byte) the stored data can be copied to an eight bit latch (a parallel device).

The data is clocked in one bit at a time. When all eight bits have been clocked in, the Parallel data is available at the output.

Parallel in, Serial Out, PISO

• First reset all the flip flops. This clears any old data.
• Now each input line is used to set each flip flop.
• An input line carrying a zero will not clear the flip flop. This is why the first reset step is required.
• Finally clock the shift register. Each bit comes out of the last flip flop.
  On the rising edge of each clock pulse, the next bit of data arrives at the output.