Decade counter (SN74LS90)
The SN74LS90 is a decade counter (divide by 10). It consists of four master-slave flip-flops and logic for binary/BCD counting. It provides QA...QD outputs; can obtain a square wave of 10 (or cycle of 10) by connecting QD to the clock input. It has synchronous reset and preset. Widely used for BCD digit counters in educational projects.
Configuration
4 BCD outputs, 2 clock inputs
Type
BCD Counter (mod-10)
Applications
BCD digit counters, Frequency dividers...
Truth Table
| Count | QD | QC | QB | QA |
|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 |
| 1 | 0 | 0 | 0 | 1 |
| 2 | 0 | 0 | 1 | 0 |
| 3 | 0 | 0 | 1 | 1 |