Basic RS flip-flop
A basic working principle of RS flip-flop
Basic RS flip-flop is shown in Figure 1 (a) below. It consists of two non-gate, closed by means of positive feedback from, you can also use two or closed doors made by way of positive feedback. Figure (b) is the basic RS flip-flop logic symbols. Also known as the basic RS flip-flop latch (Latch) triggers.Figure 1 Basic RS flip-flop circuit and logic symbols
A gate defines an input for the Rd side, active low, as a direct home
Edge D flip-flop:
Negative Edge-triggered master-slave flip-flop operation, must be added before the positive edge input signals. If the CP high interference occurs during the input signal, then it may trigger a state of error. The edge of the trigger allows the trigger along the CP before the moment came to add the input signal. Thus, the input time is shortened by the interference, the possibility of interference is reduced. Edge D flip-flop is also known to maintain - block edge D flip-flop.
Circuit Structure: The trigger NAND gate by 6, of which G1 and G2 a basic RS flip-flop.SD and RD is connected to the input of the basic RS flip-flop, which are preset and clear end, active low. When SD = 0, and RD = 1, no matter what kind of input D for the state, will cause the Q = 1, Q = 0, the flip-flop is set to 1; when the SD = 1 and RD = 0, the trigger status is 0 , SD and RD are usually referred to directly set to 1 and set to 0 end. We set them have joined the high, does not
affect circuit operation. Works as follows:
1.CP = 0, the NAND gate G3 and G4 block, its output Q3 = Q4 = 1, triggers the state change. Meanwhile, Q3 and Q4 to Q5 Q6 of the feedback signal to the two doors open, so you can receive input signal D, Q5 = D, Q6 = Q5 = D.
2. When the CP changes from 0 to 1 flip-flop flip. G3 and G4 when open, they Q3 and Q4 of input from the G5 and G6 state output state decision. Q3 = Q5 = D, Q4 = Q6 = D. RS flip-flop from the basic logic function can see, Q = D.
3. Trigger flip in the CP = 1 input signal is blocked. This is because the G3 and G4 open, they Q3 and Q4 the output of the state are complementary, that is, there must be a 0, if Q3 is 0, output by the G3 to the G5 G5 line will be the feedback input blockade, the blockade of the D flip-flop of the path leading to the basic RS; the feedback line played to trigger state and stop at 0 to 1 state of flip-flop effect, it is set to 0, the feedback line is called the maintenance line, set 1 block line. Q4 is 0, the G3 and G6 blockade, D-side path leading to the basic RS flip-flop is also blocked. Q4 output feedback to the G6 line of play to maintain a state of flip-flop effect, called the maintenance line is set to 1; Q4 output to input feedback line G3 to play the role of preventing the trigger set to 0, called the blocking line set to 0 . Therefore, the trigger is often referred to as the maintenance - blocking trigger. In short, the trigger is a positive edge in the CP input signal prior to acceptance, positive edge triggered flip, positive edge after the input Jibei block, three steps are completed at the positive edge, so it triggers the edge said. Compared with the master-slave flip-flop
With the technology edge triggers a stronger anti-interference ability and higher operating speed. Functional Description
1. State transition truth table
2. Characteristic equation Qn 1 = D1. Created: blocking by the next flip-flop of the circuit diagram can be seen to maintain, because CP signal is added to the door on the G3 and G4, which prior to the arrival gate at the rising edge of CP G5 and G6 output steady state to be established. After the input signal reaches the D-side, to go through a gate propagation delay time of G5's output state can be established, while the G6's output state to go through two gates of the transmission delay time can be established, so D side of the input signal must be arrive at the rising edge of CP, and time should be established to meet: tset 2tpd.
2. Hold time: from the next chart shows, in order to achieve edge-triggered, should ensure that CP = 1 the output of the state during the same gate G6, from D-side state changes. To this end, in the case of D = 0, when the CP have to wait after the rising edge reaches the output of gate G4 G6 low return to the gate after the input, D-side low only allowed to change. Therefore, low level input signal hold time for the tHL tpd. In the case of D = 1, the CP output rising edge will arrive G3 G4 blockade, it is not required
Input remained unchanged, so the input signal to maintain high time tHH = 3. Propagation delay time: the work of the chart is not difficult to calculate the waveforms, the arrival from the start to the rising edge of CP, the output from the high to low propagation delay time and from low to high tPHL transmission delay time tPLH are: tPHL = 3tpd tPLH = 2tpd
4. The maximum clock frequency: To ensure the composition of the gate G1 ~ G4 synchronous RS flip-flop flip reliably, CP should be greater than the duration of high tPHL, so the width of the clock signal is high should be more than tPHL tWH . In order to arrive before the next rising edge of CP gates G5 and G6 to ensure that the new output level can be firmly established, CP should not be less than the duration of low gate G4 of the transmission delay time and tset of and, that the clock signal low level width tWL tset tpd, so get:
Integrated in the actual trigger, the transmission time of each door is different, and different forms were simplified, so the results discussed above are just some
Qualitative physics. Determination of the true parameters of the experiment.
In summary, on the edge of the D flip-flop be summarized as follows:
1. Edge D flip-flop has received and the memory signals, also known as latch;
2. Edge-triggered D flip-flop means are pulse;
3. Edge D flip-flop constraints do not exist and a change phenomenon, anti-jamming performance, work fast