16-Port EIA 422A signal voltage levels
The line driver produces a differential voltage in the range of 2 to 6 volts (measured at the generator interface point). The magnitude of the differential voltage at the receiver must be in the range of 200 millivolts to 6 volts (measured at the load interface point).
Measurements are taken at terminal A (positive lead) with respect to terminal B (negative lead). The following table describes the signal states with respect to voltage levels:
| Interchange Voltage | Binary State | Signal Condition |
|---|---|---|
| + Voltage | 0 | Space |
| - Voltage | 1 | Mark |
The 16-Port Asynchronous EIA 422A adapter supports indoor cabling up to 1200 m (4000 ft) in length. Cables of such lengths are susceptible to sudden voltage surges due to induced voltages such as indirect lightning strikes. Secondary surge protection circuitry is implemented on the EIA 422A adapter to protect it from these voltage surges. The surge protection circuitry is implemented on the adapter interface data lines.
Fail-safe circuitry has been added to the input leads of each EIA 422A receiver to prevent fault conditions when the receiver is not connected to a driver (open cable). The fail-safe circuitry sets the receiver to the mark state (binary 1) whenever the receiver is not connected to a driver.
The electrical characteristics of the 16-Port asynchronous EIA 422A adapter ports comply with the EIA Standard 422A dated December 1978.