The LDM485 is a compact RS-232 to RS-485 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 RS-485 connections are made through convenient solderless screw terminals.

The LDM485 series is designed for full duplex operation over two-wire pairs. Outputs are tri-state, allowing multidropping of up to 64 units. Hardware handshake is available over two separate wire pairs. Data rates are DC to 57.6k baud. Six diagnostic LED indicators are provided (see Figure 1) 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. Also, a line termination switch connects a line termination resistor and line bias resistors to the RS-485 receive lines. The RS-485 interface supports Request To Send and Clear To Send on separate wire pairs. The LDM485 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 to screw terminals 1 and 2 on the RS-485 connector. Alternately, they can use ±12VDC to pins 9 (+) and 10 (-) of the RS-232 connector.
  • Complete Isolation with Optical Couplers and Power DC-to-DC Converter
  • Industrial Surge Protection Devices
  • Six LED Diagnostic Indicators
  • 19.2K Baud at 3 Miles (5km), 57.6K Baud at 0.5 Miles (0.8 km)
  • Request-To-Send, Clear-To-Send Handshake
  • Tri-state Outputs for Multidrop Applications, Up to 64 Devices
  • Selection of Connectors
  • Wide Operating Temperature Range
  • Solderless Screw Terminal Field Connections
  • CE Compliant
Fully Isolated RS-232/485 Converter

LDM485 Devices


Part Number Configuration
Male RS-232 connector
Male RS-232 connector, European Power Transformer
Male RS-232 connector and U.S. Power Transformer
Female RS-232 connector
Female RS-232 connector, European Power Transformer
Female RS-232 connector and U.S. Power Transformer

Frequently Asked Questions


Can Dataforth provide calibration reports for modules I purchased?
Yes we can provide calibration reports for the modules that you purchased.

You can either
a) visit https://www.dataforth.com/TestDataReport.aspx to search for Test Report Datasheets by Serial Number or
b) you can send us a list of model numbers and their serial numbers to support@dataforth.com

Can I communicate between a two LDM Converters / Line Drivers without DTR (Data Terminal Ready) control signal?
Yes, two LDM Converters / Line Drivers can be setup to communicate between two remote RS-232 terminals with only TD (Transmit Data), RD (Receive Data) and GND (Ground) signals. The setup is possible only if the communication is Simplex (one-way over two-wires) or Full-Duplex (two-way over four-wires). For Half-Duplex (two-way over two-wires) communication DTR control signal is required.

Short DTR line to RLSD (Received Line Signal Detect) on both end of RS-232 terminals at the LDM connectors. The RS-232 terminals at the LDM is a DB-25 connector. For DB-25 connectors, DTR is Pin 20 and RLSD is Pin 8.

If a DB-9 to DB-25 converter is used at the RS-232 terminal then short Pin 4 (DTR) to Pin 1 (RLSD or DCD - Data Carrier Detect) on the 9-pin connector.