7.13 Registers

Chapter 7.13 Registers

Physics Lecture Notes – Phys 395 Electronics Book
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Physics Lecture Notes – Phys 395 Electronics Book

  • CHAPTER 7. DIGITAL CIRCUITS1537.13RegistersRegisters are formed from a group of flip-flops arranged to hold and manipulate a data wordusing some common circuitry. We will consider data registers, shift registers, counters anddivide-by-N counters.7.13.1Data RegistersThe circuit shown in figure 7.26 uses the clocked inputs of D flip-flops to load data into theregister on the rising edge of a LOAD pulse.D2D1D0LOADDCQDCQDCQFigure 7.26: A data register using the clocked inputs to D-type flip-flops.It is also possible to load data and still leave the clock inputs free (figure 7.27). Theloading process requires a two-step sequence. First the register must be cleared, then it canbe loaded.NCLEARD2D1D0LOADDCSRQQDCSRQQDCSRQQFigure 7.27: A more complicated data-loading technique leaves the clocked inputs free butrequires a clear-load pulse sequence.7.13.2Shift RegistersA simple shift register is shown in figure 7.28. A register of this type can move 3-bit paralleldata words to a serial-bit stream. It could also receive a 3-bit serial-bit stream and save it