Source: https://mokxi.com/parts/74hc595 Updated: 2026-09-27 Part # 74HC595 shift register Eight outputs from three pins. Shift a byte in and latch it. or see every part - 16 pins Drawn live by the editor's own code, at the size you see it. Reference ## Every one of its 16 pins Pin Role What it does Q1 Output Q2 Output Q3 Output Q4 Output Q5 Output Q6 Output Q7 Output GND Input or output Q7S Output MR Input SHCP Input STCP Input OE Input DS Input Q0 Output VCC Input or output This part ## What it does The 74HC595 turns three signal pins into eight outputs, and the trick to understanding it is that there are genuinely two separate eight-bit registers inside. The shift register moves on every rising edge of SHCP, dropping whatever is on DS into the first stage and pushing everything else along by one; do that eight times and it holds a full byte. The storage register, the latch, is the one Q0 through Q7 actually show, and it only changes on a rising edge of STCP, which copies the shift register into it in one step. That is why the outputs sit completely still while a byte is clocked in and jump together only at the latch edge. MR clears the shift register alone, asynchronously, leaving the latch untouched; OE three-states all eight outputs without touching either register. Every edge carries the datasheet’s typical 15 nanosecond propagation delay before the pins actually move. How it is modeled ## What is true about the 74HC595 shift register, here ### 74HC595: 8-bit shift register with output latch The chip everyone reaches for when they run out of pins. Two registers inside it: an eight-stage shift register clocked by SHCP, which moves everything along and drops DS into stage 0 on a rising edge; and a storage register (the latch), which is what Q0–Q7 actually show and which only changes on a rising edge of STCP. MR (active low) clears the shift register without touching the latch; OE (active low) three-states the outputs without touching either register, so a disabled chip still shifts and its last byte is unharmed underneath. Both registers power up cleared. Propagation delay: 15 ns typical, STCP to Qn. See it in: LED bar chaser. ### Not modeled One typical delay, and nothing around it. Each chip carries a single propagation delay taken from its datasheet's typical column at VCC = 5 V, CL = 15 pF and 25 °C, and uses it for every path through the package. There is no minimum or maximum, no spread between the gates in one chip, no rise or fall time, no output slew and no dependence on supply voltage, load capacitance or temperature, all of which a real 74HC part has, and all of which a datasheet gives ranges for. On the 74HC595 the one figure is the STCP-to-Qn number used for SHCP and MR to Q7S as well, which the datasheet lists a nanosecond or two apart. No setup, hold or pulse-width checks. The 74HC74 and the 74HC595 take a clock edge whenever they see one; nothing here refuses data that changed too close to the edge or a clock pulse that was too narrow, and nothing warns about it. A real part would metastable or simply miss. No supply current, no output current limit and no bus contention damage. An output driving into another output is resolved as two drivers on one net; nothing gets hot. Sequential parts power up cleared rather than random, because a toggle divider fed Unknown never escapes it. See how faithfully a part behaves. From The 74HC logic family, in full. Projects ## See the 74HC595 shift register in a project Shown here on: Arduino Uno R3 Learn ## Where it turns up in a lesson ### In the twelve week course - Week 8: More outputs than pins: the shift register ### In a learn article - Shifting a Byte In, One Edge at a Time More parts ## The rest of the bench Every one of these is drawn and simulated the same way. Full-size breadboard A real 0.1 inch grid with the rails and the center channel, 63 columns wide. Jumper wires Drag from any pin or hole to any other. Corners snap, and you can drag them. Power A supply rail at the voltage you choose. Ground The other end of every circuit. LED Lights when current flows. Five colors, and the brightness is what your eye would see. Resistor Any value you like, with the color bands drawn to match. ESP32-C3-DevKitM-1 A RISC-V board that runs your firmware at 160 MHz on the real memory map. Pushbutton A 12 mm tactile switch. Hold it while the simulation runs. Raspberry Pi Pico The RP2040 board on our own Cortex-M0+ core. Pick a program and press Run. Raspberry Pi Pico W Raspberry Pi Pico W (RP2040). The same board and the same pinout as a Pico, with the CYW43439 on it. The WiFi is simulated (no radio, no real internet), and the on-board LED, which hangs off that chip rather than off GP25, is driven through the same path. Everything else is the Pico. STM32F411 Black Pill The Black Pill on our own Cortex-M4 core. Pick a program and press Run. BBC micro:bit V2 The nRF52833 board with its 5x5 LED matrix, buttons A and B and a speaker. Wire the rings to a breadboard. See every part ## Wire up the 74HC595 shift register Open the editor and push it into the breadboard. It is free, and it runs on your own machine. Start building Open the editor