The ISO1176 is an isolated half-duplex differential line transceiver that meets the requirements of EN 50170 and TIA/EIA 485/422 applications. The device is rated to provide galvanic isolation of up to 2500 V_RMS for 60 s per UL 1577. The device has active-high driver enable and active-low receiver enable functions to control the data flow. The device has maximum data transmission speed of 40 Mbps.

When the driver enable pin, DE, is logic high, the differential outputs A and B follow the logic states at data input D. A logic high at D causes A to turn high and B to turn low. In this case, the differential output voltage defined as V_OD = V_(A) – V_(B) is positive. When D is low, the output states reverse, B turns high, A becomes low, and V_OD is negative. When DE is low, both outputs turn high-impedance. In this condition, the logic state at D is irrelevant. The DE pin has an internal pulldown resistor to ground, thus when left open the driver is disabled (high-impedance) by default. The D pin has an internal pullup resistor to V_CC, thus, when left open while the driver is enabled, output A turns high and B turns low.

When the receiver enable pin, RE, is logic low, the receiver is enabled. When the differential input voltage defined as V_ID = V_(A) – V_(B) is positive and higher than the positive input threshold, V_IT+, the receiver output, R, turns high. When V_ID is negative and less than the negative and lower than the negative input threshold, V_IT– , the receiver output, R, turns low. If V_ID is between V_IT+ and V_IT– the output is indeterminate. When RE is logic high or left open, the receiver output is high-impedance and the magnitude and polarity of V_ID are irrelevant. Internal biasing of the receiver inputs causes the output to go failsafe-high when the transceiver is disconnected from the bus (open-circuit), the bus lines are shorted (short-circuit), or the bus is not actively driven (idle bus).