Connection problems with printer

If you connect the server with your printer, it might not work. In this FAQ entry we will show the most common reasons why it does not work and how to solve this.

  • Port does not appear
    With recent os your serial driver is normally detected out of the box. But in rare cases
    you need to install the serial driver. For linux you need a kernel
    where the driver was compiled in.
  • Which port to use
    If you do not know which
    port belongs to your printer, disconnect printer and check the offered port list. Add then the printer with main power enabled. The newly appeared port is the one you want.
  • Communication does not start
    Make sure you have selected the right firmware type. Also the baud rate must match the one selected in your printer. The most frequently used
    baud rates are 115200 and 250000 baud.
  • Still no communication
    Most printers use the signals DTR/RTS to reset the printer. But a few use these to control data flow. In these cases only on combination of low/high, high/low, low/low or high/high will make sending and receiving work. You can change them in connection configuration.
  • When printer is enabled after server I get communication errors at the start under linux
    The typical reason for this is a software called ModemManager that is often installed by default. It opens each appearing serial connection to test if it is a modem and this interferes with the servers communication. If you have no UMTS/5G modem using this you can simply uninstall it with:

    sudo apt-get remove modemmanager

    Otherwise you need to teach the ModemManager to ignore the serial connection.