74LS165 8-bit parallel-in, serial-out shift register
The 74LS165 is an 8-bit shift register that loads eight bits at once from A–H and then shifts them out one at a time on QH. With SH/LD′ low it loads; with SH/LD′ high, each rising clock edge shifts the bits one place toward QH, bringing SER in at the other end.
74LS165 pinout
Top view of the 16-pin DIP package. Pin 1 is at the bottom left, beside the notch, and the numbers run anticlockwise. Power is on pin 16 (VCC, +5 V) and pin 8 (GND).
| Pin | Name | Type | What it is |
|---|---|---|---|
| 1 | SH/LD′ | Input | Input, active-low |
| 2 | CLK | Input | Input |
| 3 | E | Input | Input |
| 4 | F | Input | Input |
| 5 | G | Input | Input |
| 6 | H | Input | Input |
| 7 | QH′ | Output | Totem-pole output, active-low |
| 8 | GND | Ground | 0 V |
| 9 | QH | Output | Totem-pole output |
| 10 | SER | Input | Input |
| 11 | A | Input | Input |
| 12 | B | Input | Input |
| 13 | C | Input | Input |
| 14 | D | Input | Input |
| 15 | CLK INH | Input | Input |
| 16 | VCC | Power | +5 V supply |
74LS165 function table
| SH/LD′ | CLK INH | CLK | What happens |
|---|---|---|---|
| 0 | X | X | Load A–H at once |
| 1 | 1 | X | Hold |
| 1 | 0 | ↑ | Shift one place toward QH, SER in at A |
| 1 | 0 | 0 | Hold |
↑ is the clock's rising edge. CLK and CLK INH are interchangeable: either can be the clock while the other is held low.
What the 74LS165 is used for
- Reading eight switches or buttons with three wires
- Parallel-to-serial conversion
- Expanding the inputs of a microcontroller, several chips chained through SER
Electrical summary
| Package | 16-pin DIP |
| Supply voltage | 5 V (4.75 V to 5.25 V) |
| Output type | Totem-pole — drives both high and low |
| Output current, low | sinks up to 8 mA |
| Output current, high | sources up to 0.4 mA |
| Input current, low | 0.4 mA out of each input held low |
| Fan-out | one output can drive about 20 LS inputs |
Typical figures for quick reference when planning a board. Check the manufacturer's datasheet for limits and timing before committing a design. The 74HC165 and 74HCT165 use the same pin numbers, with different electrical values.
The 74LS165 and the Breadboard Simulator
The 74LS165 is not in the Breadboard Simulator's parts library yet — this page is a reference. The simulator seats the gates, decoders, multiplexers, adders and buffers marked on the chips page, so the logic around a 74LS165 can be planned and wired there.