74HC165D Detailed explanation of pin function specifications and circuit principle instructions

The 74HC165D is a part of the 74HC series from Nexperia, which produces a variety of logic ICs. This specific IC is an 8-bit serial-in, parallel-out shift register, which is commonly used for expanding the number of digital input or output pins in a microcontroller circuit.

1. Device Overview:

Model: 74HC165D Family: 74HC (High-Speed CMOS) Package Type: The "D" suffix indicates that it comes in a DIP-16 package, meaning it has 16 pins.

2. Pin Function and Specification

Pin Number Pin Name Description 1 QH (Output) Serial output. The output of the shift register, carries data out bit-by-bit. 2 QH' (Inverted Output) Inverted version of the serial output, optional in some designs. 3 /PL (Parallel Load) Active low input that triggers parallel loading of data from inputs to shift register. 4 /CE (Chip Enable) Active low input used to enable the device for operation (if not active, the device is disabled). 5 Clock (Clock Input) The clock input is used to shift data through the register. Rising edge triggered. 6 VSS (Ground) Ground pin, connected to circuit ground. 7 QH (Parallel Output) Output for bit 1 of the parallel data. Can output a "1" or "0" depending on the state of the register. 8 QH' (Inverted Output) Inverted output for bit 2 of the register. 9 QH (Parallel Output) Output for bit 3 of the register. 10 QH' (Inverted Output) Inverted output for bit 4 of the register. 11 QH (Parallel Output) Output for bit 5 of the register. 12 QH' (Inverted Output) Inverted output for bit 6 of the register. 13 QH (Parallel Output) Output for bit 7 of the register. 14 VCC ( Power Supply) Power pin, connected to the supply voltage. 15 Serial Input (SI) Serial data input pin to shift data into the register. 16 Clock Enable (CE) A clock enable signal that controls whether clocking is enabled or disabled.

3. Pinout Explanation:

The 74HC165D is an 8-bit shift register with 16 pins in total. The IC can shift data in serially and output in parallel. It uses a shift register principle, where data can be loaded in parallel and shifted out serially, saving microcontroller I/O pins.

VSS (Pin 6): This is the ground pin, where the negative supply voltage (0V) should be connected. VCC (Pin 14): This is the positive supply voltage pin, typically 5V. Clock (Pin 5): The clock pin determines when the data is shifted into the shift register. A rising edge will latch the data from the shift register into the parallel outputs. /PL (Pin 3): This pin is used for parallel loading of data into the shift register. It must be low to load data. /CE (Pin 4): When this pin is low, it enables the device to function. If high, the IC is disabled. QH, QH' (Pin 1, 2): These are serial output pins used to send out data from the shift register. Serial Input (SI): This is the input for serial data that will be loaded into the shift register on each clock pulse.

4. FAQs on the 74HC165D:

1. What is the purpose of the 74HC165D shift register?

The 74HC165D is used to expand the number of digital input pins on a microcontroller by shifting data into it serially and then reading it out in parallel.

2. How does the clock input (Pin 5) work?

The clock input triggers the shifting of data into the shift register. Each rising edge of the clock shifts one bit of data.

3. What is the significance of the /PL pin (Pin 3)?

The /PL pin allows parallel loading of data from the input pins into the register. It must be low to load data.

4. What happens when the /CE pin (Pin 4) is high?

When the /CE pin is high, the shift register is disabled, and no shifting or loading of data occurs.

5. Can I use multiple 74HC165D ICs in a chain?

Yes, you can chain multiple 74HC165D ICs together, as the serial output of one can be connected to the serial input of the next.

6. What is the maximum voltage for VCC?

The typical VCC voltage for the 74HC165D is 5V. The absolute maximum is 7V, but voltages higher than 6V should be avoided to prevent damage.

7. How does the serial output (QH) work?

The QH pin outputs the data serially. After a clock pulse, one bit of data is shifted out of the register.

8. What are the possible values for the parallel output pins (QH1-QH8)?

Each parallel output pin will be either a high or low value, depending on the data loaded into the shift register.

9. What is the function of the inverted output (QH')?

The inverted output provides the complement of the serial or parallel data. It is useful in certain designs requiring inverted logic.

10. Can I use the 74HC165D for both inputs and outputs?

The 74HC165D is designed primarily for expanding input pins for a microcontroller, allowing it to read multiple switches or sensors.

11. Can the 74HC165D work with 3.3V logic levels?

Yes, the 74HC165D can work with 3.3V logic levels, but make sure to check the voltage thresholds for proper operation.

12. How fast can the shift register operate?

The speed of the 74HC165D depends on the clock frequency, but typical operation can be up to several MHz in high-speed applications.

13. Can I drive high-power devices with the 74HC165D?

No, the 74HC165D cannot drive high-power devices directly. It is meant for logic-level signals.

14. Is there any current limitation for the output pins?

Yes, the output pins of the 74HC165D are limited to a maximum current of 6mA per pin.

15. What happens if I forget to connect the VSS pin?

If the VSS pin is not connected to ground, the IC will not function properly as the circuit will lack a reference voltage.

16. How do I reset the 74HC165D?

To reset the 74HC165D, you can either use the /PL pin or ensure no data is being shifted into it and hold the clock low.

17. Can I connect the /PL pin directly to VCC?

If you connect the /PL pin directly to VCC, the device will continuously load parallel data into the register and prevent normal shifting.

18. Can I connect the /CE pin to ground permanently?

If the /CE pin is grounded permanently, the device will always be enabled and will not enter a disabled state.

19. How do I cascade multiple 74HC165D ICs?

To cascade multiple ICs, connect the QH pin of one IC to the SI pin of the next IC, and clock them in sync.

20. Is the 74HC165D compatible with TTL logic?

Yes, the 74HC165D is fully compatible with TTL logic, as it operates with standard CMOS logic levels.

This is an in-depth explanation of the 74HC165D's pin functions and circuit operation, complete with common FAQ answers. If you need further assistance with this IC or a related topic, feel free to ask!