For each clock tick, the 4-bit output increments by one. On the other hand, if clock is returned low with J=0=K, the undetermined state will persist and this cannot be exited. This 4-bit digital counter is a sequential circuit that uses JK flipflops, AND gates, and a digital clock. If the clock is set low with both J and K high, the output will continue to toggle but this can be exited by reclocking with opposing logic states at J and K. Flip Flops in Multisim Software explained with following timestamps: 0:00 - Flip Flops in Multisim Software - Digital Electronics Lecture Series0:10 - D Fli. This can be exited by setting J and K at opposing states and setting CLK back to low. If simulation is started with clock (CLK) at high state, Q and NOTQ will toggle regardless of the state of J and K. If simulation is started with clock (CLK) at low state, Q and not Q will be at undetermined state and this cannot be exited. Note, however, that in the succeeding stages the J-K flip-flops are NEGATIVE EDGE-TRIGGERED which are distinguished by BUBBLE (circle) in clock input (C) terminal. Here, there is no discrepancy between the 'book example' and your Multisim circuit. The 100 kΩ load resistors are not part of the Master-Slave J-K Flip-Flop, their purpose is to help initialize the output to known logic state. In the 'book example' the clock (C) input of the first flip-flop is connected to the Clock source. This results to a negative-edge-triggered master-slave J-K flip-flop. Next, a process to derive the clock pulse: process(Clk)Ĭlk_pulse Clk, becomes Clk => Clk_pulse.The circuit is an interconnection of a J-K latch and an S-R flip-flop in master-slave configuration. Each probe measures one bit of the output, with PR1 measuring the least significant bit and PR4 measuring the most significant bit. After it reaches its maximum value of 15 (calculated by 24-1), it resets to zero. Note that this is simulation-only code, so you can use initial values however you like. For each clock tick, the 4-bit output increments by one. We can easily shorten the clock pulse width to get rid of these oscillations by adding a new 'pulse' signal, derived from the clock: signal Clk_pulse : std_logic := '0' Apply the clock pulses and observe the output. in the next steps we will see how we can count those cycles to make up the seconds, minutes and hours of our clock. a 1 Hz clock is generating a pulse every second. You can now see the oscillations that result from too long a clock pulse in the simulation waveform: Synchronous Counter Design a 3-bit synchronous counter with the sequence below by using JK flip flops. Step 1: Building the Time Base Module The Concept behind a Digital Clock is that we are essentially counting up clock cycles. To start with, the conventional way to design a JK flip flop in VHDL would look like this: signal Q_s : std_logic
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