The LDM85 is a small, inexpensive fiber optic transmitter/receiver. It features a complete RS-232/422/423 port as well as high speed TTL data transmit and receive. It is capable of data rates from DC to 5M baud. A pair of these units allows most RS-232C cable links to be replaced and extended with a duplex fiber optic cable. The normal 50-foot RS-232 limit may be extended to 1.2 miles (2 km). Fiber optic data communications provide complete EMI/RFI rejection, isolation, elimination of ground loops, and reduced error rates. Data security is enhanced by almost nonexistent electromagnetic emissions. A unique multipoint capability allows local area networks to be formed with the isolation and data security of a fiber optic data highway.

The LDM85 is packaged in a rugged aluminum enclosure small enough to mount on the back panel of typical computer equipment, saving valuable desk and floor space. The RS-232 connection is through male or female EIA 25-pin connectors. The fiber optic connection is either through SMA (905) or ST connectors. Additional features include a TD/RD reversing switch for connection to DTE (Data Terminal Equipment) or DCE (Data Communication Equipment) ports, three diagnostic LED indicators, and locally connected handshake lines. The TTL port combined with the RS-232 port may be interfaced to RS-422/423 ports in 4-wire point-to-point mode only. Fiber optic cables may be ordered with connectors factory installed.
  • Data Rates to 5M Baud
  • RS-232, RS-422, TTL System Interfaces
  • Multipoint Capability
  • LED Indicators
  • DCE/DTE Switch
  • Small Size
  • Low Cost
  • SMA- or ST-Compatible Optic Connectors
  • 120/220VAC, +5VDC or 8 to 20VAC/DC Power
  • CE Compliant
Fiber Optic Converter

LDM85 Devices

Part Number Configuration
Pinned RS-232 connector
Pinned ST fiber optic connector
Pinned RS-232 connector, European Wall transformer, 220VAC
Pinned ST fiber optic connector, European Wall transformer, 220VAC
Pinned RS-232 connector, U.S Wall transformer, 120VAC
Pinned ST fiber optic connector, U.S Wall transformer, 120VAC
Socketed RS-232 connector
Socketed ST fiber optic connector
Socketed RS-232 connector, European Wall transformer, 220VAC
Socketed ST fiber optic connector, European Wall transformer, 220VAC
Socketed RS-232 connector, U.S Wall transformer, 120VAC
Socketed ST fiber optic connector, U.S Wall transformer, 120VAC

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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 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

Does the LDM85 come with a power supply?
All power supplies are sold separately from the LDM85. The PT3 and PT3E are compatible power supplies with the LDM85.

Will the LDM85 work with LVTTL?
Because the high/low thresholds for 5VTTL and LVTTL are the same, the LDM85 will work with this standard.

Due to resource constraints on my computer, I'm unable to open the three dimensional CAD models provided on your website. Does Dataforth provide two demensional CAD models for download as well?
Two dimensional CAD models can be generated upon customer request. Please contact Customer Service for assistance.
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Dataforth offers a wide range of custom modules for those instances when our standard commercial off-the-shelf (COTS) solutions don't quite meet your specific application needs. Contact Customer Service and Application Support to discuss design guidelines and design feasibility. Customer Service and Application Support can be reached at or +1-800-444-7644.

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