74LS194 4-bit bidirectional universal shift register
The 74LS194 is a 4-bit shift register that can shift right, shift left, load in parallel or hold, chosen by the mode inputs S1 and S0 and carried out on the rising clock edge. Shifting right moves bits from QA toward QD with SR SER coming in at QA; shifting left moves them from QD toward QA with SL SER coming in at QD.
74LS194 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 | CLR′ | Input | Input, active-low |
| 2 | SR SER | Input | Input |
| 3 | A | Input | Input |
| 4 | B | Input | Input |
| 5 | C | Input | Input |
| 6 | D | Input | Input |
| 7 | SL SER | Input | Input |
| 8 | GND | Ground | 0 V |
| 9 | S0 | Input | Input |
| 10 | S1 | Input | Input |
| 11 | CLK | Input | Input |
| 12 | QD | Output | Totem-pole output |
| 13 | QC | Output | Totem-pole output |
| 14 | QB | Output | Totem-pole output |
| 15 | QA | Output | Totem-pole output |
| 16 | VCC | Power | +5 V supply |
74LS194 function table
| CLR′ | S1 | S0 | CLK | What happens |
|---|---|---|---|---|
| 0 | X | X | X | Clear to 0 |
| 1 | 0 | 0 | X | Hold |
| 1 | 0 | 1 | ↑ | Shift right: SR SER into QA |
| 1 | 1 | 0 | ↑ | Shift left: SL SER into QD |
| 1 | 1 | 1 | ↑ | Load A–D |
↑ is the clock's rising edge.
What the 74LS194 is used for
- Shifting left or right in arithmetic circuits
- Ring and Johnson counters
- Serial-to-parallel and parallel-to-serial conversion in one chip
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 74HC194 and 74HCT194 use the same pin numbers, with different electrical values.
The 74LS194 and the Breadboard Simulator
The 74LS194 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 74LS194 can be planned and wired there.