SN74HC165DR

The SN74HC165DR from Texas Instruments is an 8-bit parallel-load shift register designed for parallel-to-serial data conversion. Eight individual direct data (A-H) inputs are enabled by a low level at the shift/load (SH/LD) input, allowing asynchronous parallel data loading. When SH/LD is held high, data shifts toward the serial QH output on each rising clock edge. The device features a clock-inhibit (CLK INH) function and a complementary QH output, providing flexible interfacing options. With a wide operating voltage range of 2V to 6V and high noise immunity, it is ideal for expanding digital inputs in microcontroller-based systems.

The SN74HC165DR operates in two modes. When SH/LD is low, the eight parallel data inputs (A-H) are asynchronously loaded into the internal register, overriding any shift operation. When SH/LD is high and CLK INH is low, each rising edge of the CLK input shifts the register data one position toward the QH output, with the SER input filling the vacated position. The clock-inhibit (CLK INH) pin can prevent shifting when held high, and its function is interchangeable with CLK. The complementary QH output provides the inverse of the QH serial output. Multiple devices can be cascaded by connecting QH to the SER input of the next stage.

• Expanding microcontroller digital input capability
• Parallel-to-serial data conversion for communication
• Keyboard, switch matrix, and DIP switch scanning
• Cascaded input expansion for PLC and industrial I/O modules
• LED display data serialization