.. _rs-485:

RS-485
^^^^^^^^^^^^^^

RS-485 expansion modules can be installed into the three (A, B, C) expansion slots for industrial I/O modules. This interface is implemented using the MAX13488 (or compatible) transceiver and interfaces with the processor's UART ports. Up to three RS-485 modules can be installed simultaneously.


Configuration and access
""""""""""""""""""""""""

Once properly installed into an I/O slot, the RS-485 interface can be accessed via the ``ttyRS485_X`` TTY device, where ``X`` is the slot name (A, B, C).

The controller also features optional software-controlled 120Ω termination resistors. The termination resistor is disabled after each power cycle. To change the termination state:

.. list-table:: RS-485: Software-controlled Termination Resistor
   :header-rows: 1

   * - SLOT
     - ENABLE TERMINATION
     - DISABLE TERMINATION
   * - A
     - ``gpioset 5 12=0``
     - ``gpioset 5 12=1``
   * - B
     - ``gpioset 5 13=0``
     - ``gpioset 5 13=1``
   * - C
     - ``gpioset 5 14=0``
     - ``gpioset 5 14=1``