The output Q 0 (LSB) changes its state (toggle) at each negative transition of the clock.
In the figure below, you can see the arrangement of a clock signal for the asynchronous Up counter when the flip-flops are negative edge triggered.įigure2.2: Timing diagram of 4-bit asynchronous binary Up counter for negative edge triggered F/Fs.įrom the above timing diagram (figure 2.2) it is clear that this 4-bit asynchronous counter counts upwards. Logic diagramįigure (2.1) shows the logic diagram of the Asynchronous Up counter for negative edge-triggered flip-flops. In this section, we will discuss the Logic diagram, Timing diagram, and operation of the Asynchronous Up counter for Negative edge-triggered flip-flops. Asynchronous Up counter for Negative edge-triggered flip-flops In this clock arrangement (figure 1.1) the counter counts upwards and is known as the Up counter. Thus, in an Up counter, each flip-flop, except the LSB flip-flop, must toggle when the inverted output (Q’) of the preceding flip-flop goes from LOW to HIGH this is clearly illustrated in figure 1.2Īlso observe that, as the D flip-flops are positive edge sensitive, the inverted output (Q’) of the preceding flip-flop acts as the clock input signal for the next flip-flop and so on. when Q 1’ goes from LOW to HIGH (because Q 1’ acts as the clock input for FF2). Q 2 (MSB) changes state (toggle) each time Q 1 goes from HIGH to LOW, i.e. when Q 0’ goes from LOW to HIGH (as Q 0’ acts as the clock input for FF1). The output Q 1 changes state (toggle) every time Q 0 goes from HIGH to LOW, i.e. The output Q 0 (LSB) changes its state (toggle) at each positive transition of the clock. Figure 1.2: Timing diagram of 3-bit asynchronous binary Up counter for positive edge-triggered F/Fs.įrom the above timing diagram (figure 1.2) it is clear that this 3-bit asynchronous counter counts upwards.