Overview: SN74HC165 8-Bit Parallel-In Serial-Out Shift Register
The SN74HC165 from Texas Instruments is a high-speed CMOS 8-bit parallel-load shift register. Designed for efficient data acquisition, it captures data from 8 parallel input lines and transmits it serially. This enables significant reduction in required I/O pins when interfacing with microcontrollers or digital systems.
Engineers widely use this device to interface button matrices, sensors, or other digital input sources to compact systems. With asynchronous parallel loading and clocked serial shifting, it offers a simple yet powerful method for digital signal acquisition. The SN74HC165 is ideal for designs requiring expanded digital inputs without increasing MCU pin usage.
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Electrical Characteristics and Timing
| Parameter | Min | Max | Unit |
|---|---|---|---|
| Supply Voltage (VCC) | 2.0 | 6.0 | V |
| High-Level Input Voltage (VIH) | 0.7 ?? VCC | ?C | V |
| Low-Level Input Voltage (VIL) | ?C | 0.3 ?? VCC | V |
| Max Input Current | ?C | 1 | ??A |
| Max Clock Frequency | ?C | 25 | MHz |
Why Choose SN74HC165 Over Other Shift Registers?
Compared to alternative parallel-in serial-out shift registers, the SN74HC165 offers faster operation with lower power consumption due to its high-speed CMOS construction. The asynchronous load capability allows for real-time input data capture, while the clock-inhibit function provides flexible control over data timing.
Its robust design supports TTL-compatible inputs and provides a straightforward logic interface. The compact DIP-16 package is highly favored for development boards, educational kits, and DIY electronics, making it an engineer-friendly component. Designers benefit from fewer MCU pins used per sensor array or button group, enabling more compact, cost-effective systems.
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Technical Parameters and Features
| Feature | Details |
|---|---|
| Function | Parallel-In Serial-Out Shift Register |
| Number of Bits | 8 |
| Logic Type | High-Speed CMOS |
| Voltage Range | 2V to 6V |
| Max Clock Frequency | 25 MHz |
| Load Type | Asynchronous Parallel Load |
| Serial Output | QH and QH?? |
| Package | DIP-16 |
| Input Compatibility | TTL and CMOS |
| ESD Protection | Yes |
Typical Applications
- Microcontroller input expansion for switches and buttons
- Digital data acquisition systems
- Low-pin-count embedded systems
- LED matrix scanning and row control
Frequently Asked Questions (FAQ)
What is the purpose of the SN74HC165?
This IC is used to collect 8 parallel input signals and shift them out serially. It helps reduce the number of microcontroller I/O pins required for reading multiple inputs.
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How is data loaded into the shift register?
The SN74HC165 supports asynchronous parallel loading. When the LOAD pin is pulled low, the parallel inputs are latched into the register on the next clock pulse.
Can it work with 3.3V microcontrollers?
Yes, it supports a supply range from 2V to 6V, making it compatible with both 3.3V and 5V logic systems.
Is the device suitable for high-speed data acquisition?
With a maximum clock frequency of 25 MHz, it performs well in high-speed applications, provided proper timing margins are observed in the design.
How does it differ from SN74HC595?
The SN74HC165 captures parallel input data and outputs it serially, while SN74HC595 is a serial-in, parallel-out shift register. They serve complementary roles in digital interfaces.



