UNLESS OTHERWISE NOTED, this document contains PRODUCTION DATA.
Table 2 shows the driver functional modes.
|VCC1||VCC2||INPUT D||DRIVER ENABLE DE||OUTPUTS(3)|
|Y, A||Z, B|
The description that follows is specific to half-duplex device but the same logic applies to full-duplex device with the outputs being Y and Z.
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 the D input causes the A output to go high and the B output to go low. Therefore the differential output voltage defined by Equation 1 is positive.
A logic low at the D input causes the B output to go high and the A output to go low. Therefore the differential output voltage defined by Equation 1 is negative. A logic low at the DE input causes both outputs to go to the high-impedance (Hi-Z) state. The logic state at the D pin is irrelevant when the DE input is logic low. The DE pin has an internal pulldown resistor to ground. The driver is disabled (bus outputs are in the Hi-Z) by default when the DE pin is left open. The D pin has an internal pullup resistor. The A output goes high and the B output goes low when the D pin is left open while the driver enabled.
Table 3 shows the receiver functional modes.
|VCC1||VCC2||DIFFERENTIAL INPUT||RECEIVER ENABLE RE||OUTPUT R|
|VID = VA – VB|
|PU||PU||–0.02 V ≤ VID||L||H|
|–0.2 V < VID < 0.02 V||L||Indeterminate|
|VID≤ –0.2 V||L||L|
|Open, Short, Idle||L||H|
The receiver is enabled when the receiver enable pin, RE, is logic low. The receiver output, R, goes high when the differential input voltage defined by Equation 2 is greater than the positive input threshold, VTH+.
The receiver output, R, goes low when the differential input voltage defined by Equation 2 is less than the negative input threshold, VTH–. If the VID voltage is between the VTH+ and VTH– thresholds, the output is indeterminate. The receiver output is in the Hi-Z state and the magnitude and polarity of VID are irrelevant when the RE pin is logic high or left open. The internal biasing of the receiver inputs causes the output to go to a failsafe-high when the transceiver is disconnected from the bus (open-circuit), the bus lines are shorted to one another (short-circuit), or the bus is not actively driven (idle bus).