Logic Level Voltage Standards
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Standard Logic Thresholds
| Level | High (1) | Low (0) |
|---|---|---|
| 5V TTL | > 2.0V | < 0.8V |
| 5V CMOS | > 3.5V | < 1.5V |
| 3.3V | > 2.0V | < 0.8V |
| 1.8V | > 1.2V | < 0.4V |
Note: A 3.3V controller can usually 'read' a 5V TTL signal, but it cannot 'send' a 5V CMOS signal.