EIA-422A Interface Circuit Wrap Test Method
Original Publication Date: 1988-Jun-01
Included in the Prior Art Database: 2005-Feb-15
This article describes an easy test method for EIA-422A interface circuit with using an LCR circuit which has equal load to the maximum length of a transmission line. The IEA-422A interface circuit has been tested with an external wrap connector so far. But, it could not be tested under full load condition by the conventional method. An improved test method uses an LCR circuit shown in Fig. 1 which is equivalent to the actual transmission line. This LCR circuit is connected instead of the wrap connector to +/- send and receive terminals of the interface circuit. Then the interface circuit can be tested as precisely as if the actual transmission line were used. If the transmission rate is relatively low, the inductance L is considered to be negligible. Thus, the equivalent circuit can be shown as Fig. 2.