74LS164 8-bit serial-in, parallel-out shift register
The 74LS164 is an 8-bit shift register. On each rising clock edge every bit moves one place along, QA to QB and so on to QH, and QA takes the AND of the two serial inputs A and B. The eight outputs show the last eight bits shifted in. CLR′ empties it at once.
74LS164 pinout
Top view of the 14-pin DIP package. Pin 1 is at the bottom left, beside the notch, and the numbers run anticlockwise. Power is on pin 14 (VCC, +5 V) and pin 7 (GND).
| Pin | Name | Type | What it is |
|---|---|---|---|
| 1 | A | Input | Input |
| 2 | B | Input | Input |
| 3 | QA | Output | Totem-pole output |
| 4 | QB | Output | Totem-pole output |
| 5 | QC | Output | Totem-pole output |
| 6 | QD | Output | Totem-pole output |
| 7 | GND | Ground | 0 V |
| 8 | CLK | Input | Input |
| 9 | CLR′ | Input | Input, active-low |
| 10 | QE | Output | Totem-pole output |
| 11 | QF | Output | Totem-pole output |
| 12 | QG | Output | Totem-pole output |
| 13 | QH | Output | Totem-pole output |
| 14 | VCC | Power | +5 V supply |
74LS164 function table
| CLR′ | CLK | A | B | QA | QB … QH |
|---|---|---|---|---|---|
| 0 | X | X | X | 0 | all 0 |
| 1 | 0 | X | X | QA0 | hold |
| 1 | ↑ | 1 | 1 | 1 | shift along |
| 1 | ↑ | 0 | X | 0 | shift along |
| 1 | ↑ | X | 0 | 0 | shift along |
↑ is the clock's rising edge. Tie A and B together to use a single serial input.
What the 74LS164 is used for
- Driving eight LEDs or a display from just two wires
- Serial-to-parallel conversion
- Running-light and LED chaser circuits
Electrical summary
| Package | 14-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 74HC164 and 74HCT164 use the same pin numbers, with different electrical values.
The 74LS164 and the Breadboard Simulator
The 74LS164 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 74LS164 can be planned and wired there.