Description
LED, as the first basic function to be completed in MCU learning, plays a very important role in MCU learners, which also called “magic lamp” by MCU learners. I believe that everyone sees most and the simplest LED circuit is the figure shown below. As shown in the figure, not only the circuit is simple, but also its operation is very simple. Gives electrical level to I/O corresponding to eight LEDs, and the corresponding LED can be on or off.
Figure 1. simple LED circuitCatalog
74HC595 Drives 8 Bits LEDS
But not all LED circuits are so simple. Some circuits will use 74HC595 chip to drive 8 LEDs or drive the 8-bit digital tube segment code, as shown in the figure below.
Figure 2. 74HC595 drives 8 LEDs
Why is a simple circuit so complicated? The reason is obvious. Before the eight LED need eight I/O, now only three I/O can drive eight LED. Let's briefly introduce 74CH595 and use it successfully to drive eight LED lights.
The 74HC595 is an 8-bit serial-in or parallel-out shift register with a storage register and 3-state outputs. Both the shift and storage register have separate clocks. The device features a serial input (DS) and a serial output (Q7S) to enable cascading and an asynchronous reset MR input.
SI is its serial data input. Q0 to Q7 are data output. SCK, is the clock for the shift register. The 595 is clock-driven on the rising edge. This means that in order to shift bits into the shift register, the clock must be HIGH. And bits are transferred in on the rising edge of the clock. RCK, is a very important pin. When driven HIGH, the contents of Shift Register are copied into the Storage/Latch Register; which ultimately shows up at the output. So the latch pin can be seen as like the final step in the process to seeing our results at the output. SQH is serial data output.
What we want to achieve now is to move the 8-bits data of SI into 74HC595 one by one under the action of SCK and RCK and present them in parallel on Q0-Q7.
Figure 3. How 74HC595 Shift Register works
Whenever we apply a clock pulse to a 595, the bits in the Shift Register move one step to the left. Below is its code.
FAQ
74HC595 is a shift register which works on Serial IN Parallel OUT protocol. It receives data serially from the microcontroller and then sends out this data through parallel pins. We can increase our output pins by 8 using the single chip.
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8-bit Shift Register 74HC595N
A shift register is a chip you can use to control many outputs (8 here) at the same time while only using a few pins (3 here) of your Arduino.
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- How does a shift register work?
Shift registers hold the data in their memory which is moved or “shifted” to their required positions on each clock pulse. Each clock pulse shifts the contents of the register one bit position to either the left or the right.
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- How 74HC595 Shift Regiester works?
The 595 has two registers (which can be thought of as “memory containers”), each with just 8 bits of data. The first one is called the Shift Register. The Shift Register lies deep within the IC circuits, quietly accepting input.
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- How does an 8 bit shift register work?
The SN74HC595N is a simple 8-bit shift register IC. Simply put, this shift register is a device that allows additional inputs or outputs to be added to a microcontroller by converting data between parallel and serial formats. Your chosen microprocessor is able to communicate with the The SN74HC595N using serial information then gathers or outputs information in a parallel (multi-pin) format. Essentially it takes 8 bits from the serial input and then outputs them to 8 pins.
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Light emitting diode connects the anode together and then connected to the power of positive is called common anode digital tube, light emitting diode connected to the cathode and then connected to the power of the cathode is called common cathode digital tube.
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- What is the difference between shift register and counter?
In a shift register, the input of element N is the output of element N-1, and all elements use the same clock. In a counter, the input of element N is the inverse of its output, and the clock of element N+1 is the output of element N.
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