Support / Knowledge Base / Using Digital I/O line to control a relay using an XStream radio

Using Digital I/O line to control a relay using an XStream radio

This guide is only applicable to the XStream family of modems.
Follow these instructions to configure two modules to pass a dry contact input to a relay output:
  1. Change the "DR" parameter to 1 on the radio connected to the relay. This instructs a radio to read its I/O line input (pin4-DTR) and transmit any transition in its state.
  2. Ensure the "CD" parameter is set to 1 or 2 on the radio connected to your dial-up modem. This affects whether the I/O line output is default to logic 1 or 0, respectively. Note that for RS232 logic 1 is -12VDC and logic 0 is +12VDC.
  3. On the DB-9 connector when pin4 (DTR) is (de-)asserted on a transmitting radio, pins 1 & 6 (DCD & DSR) are (de-)asserted on a receiving radio. Either pin 1 or 6 can be used for your I/O output.
  4. A note on the state of pin4 (DTR): the radio has an internal resistor that automatically pulls the level to -12VDC. Apply +3 to +12VDC to the relay contact to change the state of pin4 and transmit it to the other radio. Opening the relay contact will allow the pin4 voltage to return to -12VDC.
  5. There is also a "CO" parameter. "CO" is a timeout for the state of output pins 1 & 6. After "CO" seconds, pins 1 & 6 go to their default state specified by "CD." By default "CO" is disabled and the state of output pins 1 & 6 are held steady until there is a transition or power cycle.
Important: the DIP switches on the interface board will attempt to change your "CD" parameter the next time you power it on. To disable the DIP switches from rewriting "CD," install the jumper across J7 on the interface board.
Last updated: Aug 08, 2017

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