The ADM307xE are 3.3 V， low power data transceivers with ±15 kV ESD protection suitable for full- and half-duplex communication on multipoint bus transmission lines. They are designed for balanced data transmission， and they comply with TIA/EIA standards： RS-485 and RS-422. The devices have a ? unit load receiver input impedance， which allows up to 256 transceivers on a bus. Because only one driver should be enabled at any time， the output of a disabled or powereddown driver is tristated to avoid overloading the bus. The receiver inputs have a true fail-safe feature， which eliminates the need for external bias resistors and 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 ceases.