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Flip-Flops and Related Devices
Electronics Workbench Circuit Simulation

Now, we will take a look at the flip-flops that are available in the EWB parts bins. In this tutorial, you will

  • Use the Digital parts bin
  • Use the Digital ICs parts bin
  • Learn the IC flip-flops that are available for simulation
  • Observe simulated flip-flop operation


The Digital Parts Bin
The Digital parts bin is shown in Figure 8-1(a). The top row provides a selection of generic flip-flops, which include an S-R latch, J-K flip-flops with and without asynchronous preset and clear inputs, and D flip-flops with and without asynchronous preset and clear inputs, as shown in Figure 8-1(b).


(a)


(b)



(c)
Figure 8-1 Generic and specific flip-flops in the Digital parts bin.

The last item (FF) in the bottom row of the Digital parts bin is a flip-flop template that provides a selection of specific IC flip-flops from which to choose. When you drag the FF template icon onto the screen, the list appearing in the window, shown in Figure 8-1(c), includes the following devices with a description of each device:

7472 JK, 7473 JK, 7474 D, 7476 JK, 74107 JK, 74109 JK, 74112 JK, 74113 JK, 74114 JK, 74116 Latch, 74174 D, 74175 D, 74273 D, 74373 D, 74374 D, 74375 Latch, 74377 D, 74378 D, and 74379 D

When you click on a device in the template window, a pin diagram for the device will come up and you can connect to the pins just as you would to an actual IC package. For example, select the 7474 and the diagram shown in Figure 8-2 appears on the screen.


Figure 8-2 EWB pin diagram for the 7474 dual J-K edge-triggered flip-flop.


The Digital ICs Parts Bin
The Digital ICs parts bin is shown in Figure 8-3. This parts bin differs from the Digital parts bin in that it allows you to select by part number rather than by function. The list of specific flip-flops available in this parts bin is similar to that in the Digital parts bin, although there are more devices available.


Figure 8-3 Digital ICs parts bin.


Simulated Flip-flop Operation
Figure 8-4 shows a setup for clocking a J-K flip-flop in the toggle mode. The clock is generated by a 1 kHz clock pulse generator. The J and K inputs are connected to a HIGH level using the VCC source from the Sources parts bin. On the logic analyzer, the top waveform is the clock and the bottom waveform is the Q output of the flip-flop.



Figure 8-4 EWB simulation of the toggle operation of a generic J-K flip-flop.


One-Shot and Timer
A generic one-shot (mono) and a 555 timer are available in the Mixed ICs parts bin shown in Figure 8-5.


Figure 8-5 One-shot and 555 timer in the Mixed ICs parts bin.


EWB Exercises

  1. Open EWB. (a) Select each of the generic flip-flops in Figure 8-1 and place them on the screen. (b) Using the flip-flop template, select each of the specific IC flip-flops and place them on the screen.
  2. Connect flip-flop and instruments as shown in Figure 8-4, run it using the indicated setting for the word generator, and observe the logic analyzer display.
  3. Replace the generic flip-flop in Exercise 2 with a 74112 flip-flop and repeat.
  4. Connect the generic D flip-flop to the word generator and program the instrument to produce a clock waveform and a D input waveform that alternates between a 1 and a 0 on every other clock pulse. Observe the output and verify that the setup is operating properly.
  5. Set up the one-shot to measure its output pulse width with the oscilloscope.
  6. Set up the 555 timer to produce a 100 kHz output and check it with the oscilloscope. Follow Example 8-14 in the Digital Fundamentals With VHDL textbook.



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