74LS93 4-bit binary counter
The 74LS93 is an asynchronous 4-bit binary counter: a divide-by-2 stage (CKA to QA) and a divide-by-8 stage (CKB to QB, QC, QD) that count on the falling edge. Connect QA to CKB and clock CKA, and QD QC QB QA counts 0 to 15. With both reset inputs high, every output goes to 0. VCC is pin 5 and GND is pin 10.
74LS93 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 5 (VCC, +5 V) and pin 10 (GND).
| Pin | Name | Type | What it is |
|---|---|---|---|
| 1 | CKB | Input | Input |
| 2 | R0(1) | Input | Input |
| 3 | R0(2) | Input | Input |
| 4 | NC | — | Not connected |
| 5 | VCC | Power | +5 V supply |
| 6 | NC | — | Not connected |
| 7 | NC | — | Not connected |
| 8 | QC | Output | Totem-pole output |
| 9 | QB | Output | Totem-pole output |
| 10 | GND | Ground | 0 V |
| 11 | QD | Output | Totem-pole output |
| 12 | QA | Output | Totem-pole output |
| 13 | NC | — | Not connected |
| 14 | CKA | Input | Input |
74LS93 function table
| R0(1) | R0(2) | QD QC QB QA |
|---|---|---|
| 1 | 1 | 0 0 0 0 |
| 0 | X | counts |
| X | 0 | counts |
For a 4-bit count, connect QA to CKB and clock CKA; the outputs step on each falling edge of CKA.
What the 74LS93 is used for
- Counting 0 to 15 in binary
- Dividing a frequency by 2, 8 or 16
- Counters that stop at any value, by decoding it onto the reset inputs
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 74LS93 and the Breadboard Simulator
The 74LS93 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 74LS93 can be planned and wired there.