What is 74LS74 Dual D Flip Flop?
12 December 2023
Ⅲ. Pin configuration and functions of 74LS74
Ⅳ. What are the features of 74LS74?
Ⅴ. Structure and working principle of 74LS74
Ⅵ. Technical parameters of 74LS74
Ⅶ. What are the applications of 74LS74?
The 74LS74 is a dual D flip-flop with a variety of applications. This article will introduce the 74LS74 pin configuration and functions, features, structure and working principle, technical parameters and applications, so that you can better understand this dual D flip-flop.
D flip-flop is an information memory device with memory function and two stable states for storing 1-bit binary data. It is the most basic logic unit that constitutes a variety of timing circuits, but also an important unit circuit in digital logic circuits. Therefore, D flip-flop has a wide range of applications in digital systems and computers. Flip-flop has two stable states, i.e. 0 and 1. Under the action of external signals, it can flip from one stable state to another.
The D flip-flop (data flip-flop or delay flip-flop) consists of four and non-gates, of which G1 and G2 form the basic RS flip-flop. When the master-slave flip-flop operates in level-trigger mode, the signal must be input before the signal jump edge comes. If a disturbing signal is present at the input during a CP high, the state of the flip-flop may be erroneous. However, edge triggers allow the signal to be input a split second before the CP trigger edge of the clock. This greatly reduces the time for the input to be disturbed, thus reducing the possibility of interference. An edge D flip-flop is also known as a sustain-blocking edge D flip-flop. An edge D flip-flop can be made by connecting two D flip-flops in series, but the CP of the first D flip-flop needs to be inverted using a non-gate.
74LS74 is a double D flip-flop chip manufactured by Fairchild Semiconductor. It can be used as an oscillator, register, shift register, and frequency division counter. It has the characteristics of low power consumption, high noise rejection ratio and wide operating voltage range, making it widely used in digital circuit design. Each device contains two identical, independent edge trigger circuit blocks.
Replacements and equivalents:
• HEF40312B
• MC74F74
• SN74ALS74
• 74HCT74
• 74LVC2G80
The 74LS74 has 16 pins and their names and functions are as follows.
Pin 1 (1CLR (bar)): Resets the flip flop by clearing its memory
Pin 2 (1D): Input pin of the flip flop
Pin 3 (1CLK): These pins must be provided with clock pulse for the flip flop.
Pin 4 (1PRE (bar)): Another input pin for flip flop
Pin 5 (1Q): Output pin of the flip flop
Pin 6 (1Q’(bar)): Inverted output pin of flip flop
Pin 7 (Vss): Connected to the ground of the system
Pin 8 (2Q’(bar)): Inverted output pin of flip flop
Pin 9 (2Q): Output pin of the flip flop
Pin 10 (2PRE (bar)): Another input pin for flip flop
Pin 11 (2CLK): These pins must be provided with clock pulse for the flip flop.
Pin 12 (2D): Input pin of the flip flop
Pin 13 (2CLR (bar)): Resets the flip flop by clearing its memory
Pin 14 (Vdd/Vcc): Powers the IC typically with 5V
• The activation process is straightforward, and the speed of its response is rapid.
• It adopts dual D flip-flop IC package configuration.
• The module's minimum high-level input voltage value is two volts.
• 74LS74 requires a stable power supply voltage to work properly and has higher requirements for power management.
The 74LS74 flip-flop is equipped with a pair of D flip-flops, each featuring two input terminals (D and clock) and two output terminals (Q and /Q). These D flip-flops operate with a positive edge trigger, meaning that data is refreshed during the rising edge of the clock signal.
When the rising edge of the clock arrives, the value of the input signal D will be stored inside the gate-level transmission gate of the D flip-flop. When the rising edge of the clock arrives, the value stored inside the D flip-flop will be updated according to the type of flip-flop, and the updated value will be output through the output terminals Q and /Q.
The picture below is the technical parameters of SN74LS74AN.
1. What are the applications of 74LS74?
• Locking device
• Clock divider
• Snubber circuit
• Pulse generator
• Shift register device
• Latching mechanism
• FSK modulation circuit
2. 74LS74 typical application circuit
The picture above is a remote control circuit composed of 74LS74. The power supply of this circuit uses a capacitor step-down half-wave rectifier circuit. Safety needs to be paid attention to when making this design. Usually, since the circuit board has 220V mains power, we should ensure correct operation. We plug the power plug of the household appliance that requires remote control into the power socket Cz, and then we can start using it. Each key on the remote control transmitter has a unique transmission code, resulting in distinct effects when using each key. In addition, the button technique and operation method will also affect the control.
Frequently Asked Questions
1. What is 7474 IC?
The 7474 is an edge-triggered device. The Q output will change only on the edge of the input trigger pulse. The small triangle on the clock (Cp) input of the symbol indicates that the device is positive edge-triggered.
2. What does a 74LS74 do?
The IC 74LS74 is the double D type edge-triggered category of flip flops comprise of clear preset and complementary output terminals. It has the ability to store data in the form of binary numbers and it also comes with features that stored data can be changed when required.
3. How to use 74LS74?
Operating a Flip-Flop is straightforward. Power the IC using the Vcc and GND pins. As mentioned earlier, each flip-flop functions independently. Connect the input signals to pins 2 and 3 to engage the first flip-flop, with the output reflected on pins 5 and 6.
4. What does circle mean on a 74LS74?
The triangle indicates that the clock signal is an edge-triggered signal. The circle indicates that the signal is low-active (ie., inverted). The 74LS74 has a positive-edge trigger clock (low to high).
5. How does a dual D flip-flop work?
The D flip-flop captures the value of the D-input at a definite portion of the clock cycle (such as the rising edge of the clock). That captured value becomes the Q output. At other times, the output Q does not change. The D flip-flop can be viewed as a memory cell, a zero-order hold, or a delay line.
