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.

  • After a while I only get timeouts in console
    We detected that on linux systems the drivers for some serial chips might get into a problematic state where they only send data but won’t receive anything which then causes the timeouts you see. Starting with version 0.94.3 we have added an option on linux versions to reset the usb connection forcing the driver to restart. You find this in the serial connection definition under the name “USB Reconnect on Timeout”.
    Enable it and try if this fixes the problem when detected. Some serial driver/printer combinations will
    cause the printer to reset, so the help if not as good as for the combinations where it is possible to restart without reset. In that case a print would continue after a short pause.