Basic knowledge of trigger (Part 2)

Welcome to learn digital circuit ——D trigger .

Here we will explain D Triggers and integration edges D trigger 74LS74, I hope that through our study, you will better understand the mystery of digital circuits .

Catalog

  One 、D trigger

1.D The circuit composition and logic function of the trigger

（1） Circuit structure and graphical symbols

（2） logic function

2. Integrated edge D trigger

（1） Pin arrangement and graphical symbols

（2） logic function

Two 、 Trigger knowledge dry goods

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  One 、D trigger

1.D The circuit composition and logic function of the trigger

（1） Circuit structure and graphical symbols

As shown in the figure ：

  In sync RS Based on the trigger , NAND gate G3 Output Receive the NAND gate G4 The input of R, send R=, Thus avoiding ==0 The situation of . And will NAND gate G3 Of S End changed to D Input end , That is to say D trigger .

（2） logic function

D A trigger has only one input , Eliminate the indefinite state of the output .D The trigger has a set 0、 Set up 1 The logical function of , As shown in the figure ：

  It can be seen from the picture that ,

stay CP=0 period ：

NAND gate G3、G4 By CP The low level of the terminal is off , Disable the input signal ,==1, basic RS The trigger remains in its original state .

stay CP=1 period ：

① Set up 0 function

When D=0 when , NAND gate G3 Output =1、G4 Output =0, Basically RS The trigger output is set to 0.

② Set up 1 function

When D=1 when ,  NAND gate G3 Output =0、G4 Output =1, Basically RS The trigger output is set to 1.

As shown in the figure ：

  In the 3 individual CP During pulse action , because D The change of causes the state of the trigger to change many times , There is somersault , send CP The pulse loses the meaning of synchronization . So in practice , Often use edges D trigger .

Next, let's learn the last trigger ： Integrated edge D trigger .

2. Integrated edge D trigger

（1） Pin arrangement and graphical symbols

74LS74 The chip is Integrated double rising edge D trigger , As shown in the figure ：

 CP It is the clock input ;D For data input ;Q、 Complementary output ; It is the direct reset end , Low level active ; It is the direct setting end , Low level active ; and Used to set the initial state .

（2） logic function

As shown in the table , Is the integrated double rising edge D trigger 74LS74 My menu , In the table “↑” Indicates that the rising edge triggers .

 、 It is often used as the initial state of setting trigger . Integrate D The logic function of the trigger is the same as that described above D Triggers are basically the same , The difference is that it only CP Working at the rising edge .

Two 、 Trigger knowledge dry goods

 

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That's all for the trigger , In the next issue, we will continue to explain the sequential logic circuit ！🥰🥰