The ADM4857ARZ is a RS-485/RS-422 Differential Line Transceiver suitable for high speed full-duplex data communication on multipoint bus transmission lines. The ADM4857 has dedicated differential line driver outputs and receiver inputs. The parts have 1/8-unit-load receiver input impedance, which allows up to 256 transceivers on one bus. Because only one driver should be enabled at any time, the output of a disabled or powered-down driver is three-stated to avoid overloading the bus. The receiver inputs have a true fail-safe feature, which ensures a logic high output level when the inputs are open or shorted. This guarantees that the receiver outputs are in a known state before communication begins and when communication ends. The driver outputs are slew-rate limited to reduce EMI and data errors caused by reflections from improperly terminated buses. Excessive power dissipation caused by bus contention or by output shorting is prevented with a thermal shutdown circuit.
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