All MicroE digital encoders have quadrature outputs that are compatible with 422 line receivers. The 422 data transmission standard (ANSI TIA/EIA-422, formally) is a balanced scheme for transmitting digital data over long distances with very good noise immunity. In this scheme, the driver D takes a single signal and generates two complementary or differential signals. These are then sent out over a twisted pair transmission line and received by the receiver R where they are recombined back into the original signal. This arrangement does an excellent job of eliminating common mode noise. Since this noise component will be identical in magnitude and sign on both signals, the difference between these signals will remain unchanged. The 485 standard is similar in almost all respects with the exception that it supports multiple drivers while 422 supports only one. For the purposes of this report, we will limit discussion to 422.
In general, 422 driver outputs (A+ and A-) should not exceed ±6V with respect to ground. The differential voltage between them should be greater than ±2V but not exceeding ±10V. By the time the signal pair reaches the receiver, the differential voltage must be greater in magnitude than 200mV (input sensitivity) to get valid state changes.
The role of cable termination in any data transmission scheme is to eliminate or at least minimize signal reflections. Signal reflections are a result of impedance mismatching. When a signal, traveling down a line with a certain characteristic impedance (typically around 100Ω, meets a different impedance at the far end, it will be reflected back to the source. This reflection then encounters another impedance mismatch back at the source generating aditional reflections and so on. Four different termination techniques will be discussed in this report: No Termination, Series Termination, Parallel Termination and AC Termination.