74LS76 Dual JK flip-flop with preset and clear
The 74LS76 holds two independent JK flip-flops that act on the falling edge of the clock. J sets, K resets, both together toggle, and neither holds. Note the unusual supply pins: VCC is pin 5 and GND is pin 13, not the corners.
74LS76 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 5 (VCC, +5 V) and pin 13 (GND).
| Pin | Name | Type | What it is |
|---|---|---|---|
| 1 | 1CLK | Input | Input |
| 2 | 1PRE′ | Input | Input, active-low |
| 3 | 1CLR′ | Input | Input, active-low |
| 4 | 1J | Input | Input |
| 5 | VCC | Power | +5 V supply |
| 6 | 2CLK | Input | Input |
| 7 | 2PRE′ | Input | Input, active-low |
| 8 | 2CLR′ | Input | Input, active-low |
| 9 | 2J | Input | Input |
| 10 | 2Q′ | Output | Totem-pole output, active-low |
| 11 | 2Q | Output | Totem-pole output |
| 12 | 2K | Input | Input |
| 13 | GND | Ground | 0 V |
| 14 | 1Q′ | Output | Totem-pole output, active-low |
| 15 | 1Q | Output | Totem-pole output |
| 16 | 1K | Input | Input |
74LS76 function table
| PRE′ | CLR′ | CLK | J | K | Q | Q′ |
|---|---|---|---|---|---|---|
| 0 | 1 | X | X | X | 1 | 0 |
| 1 | 0 | X | X | X | 0 | 1 |
| 0 | 0 | X | X | X | 1* | 1* |
| 1 | 1 | ↓ | 0 | 0 | Q0 | Q0′ |
| 1 | 1 | ↓ | 1 | 0 | 1 | 0 |
| 1 | 1 | ↓ | 0 | 1 | 0 | 1 |
| 1 | 1 | ↓ | 1 | 1 | toggle | toggle |
| 1 | 1 | 1 | X | X | Q0 | Q0′ |
↓ is the clock's falling edge. 1* — both outputs high while PRE′ and CLR′ are both low, which does not last once they are released.
What the 74LS76 is used for
- Toggle flip-flops for counters and frequency dividers
- State machines, where J and K make the next-state logic simpler than D
- Storing one bit with separate set and reset
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 74HC76 and 74HCT76 use the same pin numbers, with different electrical values.
The 74LS76 and the Breadboard Simulator
The 74LS76 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 74LS76 can be planned and wired there.