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TTL will always remain between the limits of 0V and Vcc, which is often 5V or 3.3V(usually for historical reasons and nomenclature, TTL refers to 5v, LVTTL refers to 3.3v, but that’s besides the point here). Here is a basic circuit for UART through TTL:
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Differential Signals: Similar to RS-422, with differential in two lines (A and B) to improve common mode noise immunityrejection
Multi-Point Communication: Allows up to 32 devices to communicate on the same bus
Half-Duplex and Full-Duplex: Can be used in half-duplex mode (one direction at a time) or full-duplex mode (simultaneous two-way communication with additional lines)
Long Distance: Suitable for very long distances, typically up to 1200 meters (4000 feet)
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