OMEGA Engineering, Inc. Fully Isolated Limited Distance Modem LDM422 Series

The LDM422 is a compact RS-232 to RS-422 converter which features a complete electrical isolation barrier and heavy duty electrical surge protectors. These devices feature a rugged aluminum enclosure small enough to mount on the back panel of typical computer equipment, saving valuable desk and floor space. Isolation is provided by optical couplers and a DC-to-DC converter. The RS-232 connection is through male or female EIA 25-pin connectors. The RS422 connections are made through convenient solderless screw terminals. The LDM422 series is designed for full duplex operation over two-wire pairs. Outputs are tri-state, allowing multidropping of up to 32 units. Hardware handshake is available over two separate wire pairs. Data rates are 75 to 19,200 baud. Six diagnostic LED indicators are provided for installation guidance and system troubleshooting. The RS-232 interface supports Request To Send, Clear To Send, Data Set Ready, Received Line Signal Detect, and Data Terminal Ready. A convenient null modem switch is provided for the data lines. The RS-422 interface supports Request To Send and Clear To Send on separate wire pairs. The LDM422 may be used to convert two sets of send and receive channels by using RTS and CTS circuits as the second data channels. Data rates are the same. The units use 12VAC from a wall-mounted transformer or 12VDC to pins 9 (+) and 10 of the RS-232 connector. The LDM422 conforms to EIA RS-232 and RS-422 specifications. Data Terminal Ready must be asserted by the host RS-232 port before the LDM422 can transmit data. When Data Terminal Ready is not asserted all outputs of the LDM422 are high impedance, allowing up to 32 LDM422 units to be multidropped on a common communications cable. See Figure on page 2 for details. Request To Send and Clear To Send are carried through the RS-422 port as two separate wire pairs. These may be used for full duplex flow control.