74LS373 Octal transparent latch, three-state
The 74LS373 holds eight D latches with a shared enable C. While C is high the outputs follow the inputs; when C goes low they hold the last value. The active-low output control OC′ disconnects all eight outputs, so the latch can sit on a shared bus.
74LS373 pinout
Top view of the 20-pin DIP package. Pin 1 is at the bottom left, beside the notch, and the numbers run anticlockwise. Power is on pin 20 (VCC, +5 V) and pin 10 (GND).
| Pin | Name | Type | What it is |
|---|---|---|---|
| 1 | OC′ | Input | Input, active-low |
| 2 | 1Q | Output | Three-state output |
| 3 | 1D | Input | Input |
| 4 | 2D | Input | Input |
| 5 | 2Q | Output | Three-state output |
| 6 | 3Q | Output | Three-state output |
| 7 | 3D | Input | Input |
| 8 | 4D | Input | Input |
| 9 | 4Q | Output | Three-state output |
| 10 | GND | Ground | 0 V |
| 11 | C | Input | Input |
| 12 | 5Q | Output | Three-state output |
| 13 | 5D | Input | Input |
| 14 | 6D | Input | Input |
| 15 | 6Q | Output | Three-state output |
| 16 | 7Q | Output | Three-state output |
| 17 | 7D | Input | Input |
| 18 | 8D | Input | Input |
| 19 | 8Q | Output | Three-state output |
| 20 | VCC | Power | +5 V supply |
74LS373 function table
| OC′ | C | D | Q |
|---|---|---|---|
| 0 | 1 | 1 | 1 |
| 0 | 1 | 0 | 0 |
| 0 | 0 | X | Q0 |
| 1 | X | X | Z |
Z is high impedance: the output is disconnected.
What the 74LS373 is used for
- Holding the low address byte on a multiplexed address/data bus
- Capturing a byte from a bus
- Driving eight LEDs that keep showing a value
Electrical summary
| Package | 20-pin DIP |
| Supply voltage | 5 V (4.75 V to 5.25 V) |
| Output type | Three-state — drives high and low, or disconnects when disabled |
| Output current, low | sinks up to 24 mA |
| Output current, high | sources up to 2.6 mA |
| Input current, low | 0.4 mA out of each input held low |
| Fan-out | one output can drive about 60 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 74HC373 and 74HCT373 use the same pin numbers, with different electrical values.
The 74LS373 and the Breadboard Simulator
The 74LS373 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 74LS373 can be planned and wired there.