Black Box MD940A Fiber Driver RS‑232 to ST Multimode, DB25, Used Working

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Black Box Fiber Driver module (MD940A series) for extending RS‑232 over multimode fiber using ST connectors, in good working used condition.
Provides asynchronous, bidirectional RS‑232 transmission over optical fiber with DTE/DCE selection.

Item details

• Brand: Black Box

• Model series: Fiber Driver (MD940A family, DB25 and dual ST‑style fiber ports)

• Type: RS‑232 serial to fiber optic extender / converter

• Serial interface:

  • RS‑232, DB25 connector (male or female depending on sub‑model; see photos)

  • Switch‑selectable DTE/DCE mode so it can emulate a terminal or modem without special cables.

• Fiber interface:

  • Two ST‑type multimode fiber connectors labeled INPUT and OUTPUT (TX/RX)

• Data rate: Transparent asynchronous transmission up to 76.8 kbps.

• Distance: Up to about 2.5 miles (4 km) over 50/62.5/100 µm multimode fiber, depending on cable and loss.

• Power: External mini‑phone style power jack (wall adapter not included; see datasheet for voltage range, typically autosensing 110–220 VAC via PSU).

• Features: XON/XOFF flow control, jumpers for high‑speed filtering and signal pull‑ups, small inline metal enclosure.

Condition

• Used, in good working condition with visible cosmetic wear (scratches, finish marks) on housing.

• Connectors (ST fiber, power jack, DB25) appear intact with no obvious damage.

• No power supply, fiber cables, or serial cables included; module only.

Notes

• Designed to be used in pairs: one Fiber Driver at each end of the fiber link, each connected to an RS‑232 device.

• DTE/DCE toggle must be set correctly for each attached device; consult the MD940A manual for configuration and jumper options.

• Suitable for extending RS‑232 connections in electrically noisy or long‑distance environments such as industrial control or data rooms.