Knowledgebase:
FiberPlex TD-1280/81 & TD-1580/81 Configurations
Posted by Danny Staub, Last modified by Danny Staub on 01 August 2019 01:30 PM
The FiberPlex TD-1280/81 & TD-1580/81 units can be used 'back to back' in many configurations.




A couple of notes, however:

  • The TD-1280 is not a DTE unit, it is pinned out to connect to a DTE. This is clearly identified in the user manual, which can be found here.
  • Take note of the pinout chart on page 6. On the 1280, pin 2 is a Send Data INPUT and pin 3 is Send Data OUTPUT.
  • When used back to back they act as null modems. In this config, where they have decided to use two 1280, a signal input on pin 2 on one unit will be presented as an output on pin 3 of the other unit for example. Same is true for all paired signals – SD/RD, RTS/CTS, DSR/RR, ST/TT. Other single direction signals will just get lost in the back to back config and are only valid in a 1280 <-> 1281 config.
  • You have advised him to cross pins 24 and 25, those two signals (TT and TM) are unrelated and will not cross
  • These units are ‘transparent’ meaning none of the controls and clocks are used to receive the data, they are just passed through to the other side, therefore they can carry any kind of signaling


Below is a table showing all of the valid connections and signal flow in this situation where you are connecting (2) TD-1280 back to back:




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