The 74HC595 is a high-performance silicon gate CMOS with 8-bit serial input / serial or parallel output shift register latch and three state output.
What is 74HC595 IC
The 74HC595 consists of an 8-bit shift register and an 8-bit D-type latch with three state parallel output. The shift register receives serial data and provides serial output. The shift register also provides parallel data to the 8-bit latch. The shift register and the latch have independent clock inputs. The device also resets the shift register asynchronously.
The 74HC595 shift register interfaces directly with the SPI serial data port on the CMOS MPU and MCU.
74HC595 Pinout &Configuration
74HC595 pinout’s image is given, as well as the details shown in the table.
|Pin Number||Pin Name||Description|
|1,2,3,4,5,6,7||Output Pins (Q1 to Q7)||The 74hc595 has 8 output pins out of which 7 are these pins. They can be controlled serially|
|8||Ground||Connected to the Ground of the circuit|
|9||(Q7) Serial Output||This pin is used to connect more than one 74hc595 as cascading|
|10||(MR) Master Reset||Resets all outputs as low. Must be held high for normal operation|
|11||(SH_CP) Clock||This is the clock pin to which the clock signal has to be provided from MCU/MPU|
|12||(ST_CP) Latch||The Latch pin is used to update the data to the output pins. It is active high|
|13||(OE) Output Enable||The Output Enable is used to turn off the outputs. Must be held low for normal operation|
|14||(DS) Serial Data||This is the pin to which data is sent, based on which the 8 outputs are controlled|
|15||(Q0) Output||The first output pin.|
|16||Vcc||This pin powers the IC, typically +5V is used.|
- Output Drive Capability: 15 LSTTL Loads
- Outputs Directly Interface to CMOS, NMOS, and TTL
- Operating Voltage Range: 2.0 to 6.0 V
- Low Input Current: 1.0 A
- High Noise Immunity Characteristic of CMOS Devices
- In Compliance with the Requirements Defined by JEDEC Standard No. 7A
- ESD Performance: HBM 2000 V; Machine Model 200 V
- Chip Complexity: 328 FETs or 82 Equivalent Gates
- Improvements over HC595
- Improved Propagation Delays
- 50% Lower Quiescent Power
- Improved Input Noise and Latchup Immunity
- These are Pb-Free Devices
How does a 74HC595 IC work?
As mentioned before, the 74HC595 is an 8-bit serial input parallel output shift register, that is, it can continuously receive (input) data and control 8 output pins in parallel. This is convenient when there are not enough GPIO pins on our MCU / MPU to control the required number of outputs. It is usually used in projects where a relatively large number of LEDs have to be controlled by microcontrollers.
It can also be used as an interface for LCD screens, as they can be used as data bits for LCD displays. Since the high level voltage is only 3.15, it can also be used to control 5V load through 3.3V microcontroller, such as relay. Therefore, if you are looking for an IC to store on the GPIO pin of the microcontroller, the IC may be the right choice for you.
The 74HC595 shift register is usually used with a microcontroller or microprocessor to expand the gipo function. Only 3 pins need to be connected to MCU, instant clock, data and latch. It has a wide operating voltage of 2V to 6V. The application circuit of the IC is shown in the figure below:
Pins 11, 14, and 12 are connected to the GPIO pins of the microcontroller. In which pin 11 does the clock send a constant pulse to maintain timing. Pin 14 is data that actually sends data about which output pins must be kept low and which pins should be raised. Pin 12 is the latch. When the pin becomes high, the received data will be updated to the output pin, and the pin can also be permanently high. For example, the binary value 0b10110011 is passed here to the microcontroller. The main reset (MR) pin is used to reset the output and keep it high to VCC when not in use. Similarly, it should also be kept low when not in use.
Another important advantage of the 74HC595 IC is that it can be cascaded to control more than eight outputs. To do this, we use Q7 ‘(pin 9), which should be connected to the data pin of the second 74HC595 IC. In this way, the first 8 bits sent from MCU will be used by the first IC, and the second 8 bits will be used by the second IC.
Circuit schematics can help us better understand how to use or work components or chips in a circuit. It is a reference to make them work in the actual circuit.
The above 74ls74 circuit schematic is for reference only.
- Expand the GPIO pin on a MCU/MPU
- LED Matrix/Cube Projects
- Interface LCD
- Cascading applications
- High logic level controller
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