74HC595

The 74HC595 is an 8-bit serial-in/parallel-out shift register with an integrated storage register (latch) and three-state outputs. It belongs to the 74HC family of high-speed CMOS logic devices and is commonly used to expand microcontroller I/O without increasing the number of I/O pins.

Key features and pins include: DS for serial data input; SH_CP as the shift register clock input; ST_CP as the storage/latch clock input; Q0–Q7 as parallel outputs; Q7’ as a serial data output for daisy-chaining; OE as an active-low output enable; and SRCLR (master reset) as an asynchronous clear that resets both the shift and storage registers. When SRCLR is asserted, all outputs go to zero; OE must be low to enable the outputs.

Operation generally involves shifting data into the device on the rising edge of SH_CP, with each bit moving through the internal shift register. A rising edge on ST_CP transfers the contents of the shift register to the storage register, updating Q0–Q7. The Q7’ output can be used to connect to the DS input of another 74HC595 for cascading multiple devices.

Electrical characteristics typically include a supply voltage range from 2 to 6 volts (with 4.5 to 5.5 volts common practice for many applications) and standard CMOS input thresholds. The device is compatible with standard CMOS/TTL logic levels and is available in various packages, such as DIP-16 and surface-mount variants.

Applications include expanding I/O for microcontrollers, LED and display drivers, and simple daisy-chained shift-register-based solutions for controlling multiple outputs with minimal IO pins.