Volume II: Troubleshooting - Communication

Electrical Characteristics

U.S. Electronic Industries Association electrical specifications are included in this section. EIA Standards are available from the EIA Engineering Department, Standard Sales, 2001 Eye Street, N.W., Washington, D.C. 20006.

For data interchange circuits, the signal shall be considered in the marking condition when the voltage (V1) interchange circuit measured at the interface point, is more negative than minus three volts with respect to Circuit AB (Signal Ground). The signal shall be considered in the spacing condition when the voltage (V1) is more positive than plus three volts with respect to circuit AB. The signal state in not uniquely defined when the voltage (V1) is in this transition region.

For data interchange circuits, the signal shall be considered in the marking condition when the voltage (V1) on the interchange circuit, measured at the interface point, is more negative than minus three volts with respect to Circuit AB (Signal Ground). The signal shall be considered in the spacing condition when the voltage (V1) is more positive than plus three volts with respect to circuit AB. The region between plus three volts and minus three volts is defined as the transition region. The signal state in not uniquely defined when the voltage (V1) is in this transition region.

During the transmission of data, the marking condition shall be used to denote the binary state ONE and the spacing condition shall be used to denote state ZERO.

For either binary state, the magnitude of the differential voltage (V0) measured between the two generator output terminals shall not be less than 6.0 volts; nor shall the magnitude of V0a and V0b measured between the two generator output terminals and generator circuit ground be more than 6.0 volts.

For either binary state, the magnitude of the voltage (V0) measured between the generator output terminal and generator circuit ground shall not be less than 4.0 volts nor more than 6.0 volts. For the opposite binary state, the polarity of V0 shall be reversed.

The following circuits are classified as Category I circuits: SD, RD, TT, ST, RT, RS, CS, RR, TR, and DM.

For applications where the signaling rate on the data interchange circuits (Circuits SD and RD) is 20,000 bits per second or less, the individual Category I circuits shall use either the balanced electrical characteristics of RS-423, without the cable termination resistance (Rt), or the unbalanced electrical characteristics of RS-422-A. Two leads shall be brought out to the interface connector for each Category I circuit. Each interchange circuit consists of a pair of wires interconnecting a balanced or unbalanced generator and a differential receiver.

For applications where the signaling rate on the data interchange circuits (Circuits SD and RD) is above 20,000 bits per second, all Category I circuits shall use the balanced electrical characteristics of RS-422. Use of optional cable termination resistance (Rt) permitted. Each interchange circuit consists of a pair of wires interconnecting a balanced generator and a differential receiver.

All other circuits are classified as Category II circuits. For all applications, Category II circuits shall use the unbalanced electrical characteristics of RS-423. Each Category II interchange circuit consists of one wire interconnecting an unbalanced generator and a differential receiver.