COM port problems and JMRI

Billybob Experimenter is back again with methods to check what may be wrong with operating system COM port problems. This came about after a member of the groups.io forum reported that he had lost computer connectivity to his layout. The member had not yet reported much concerning his hardware so it was a little difficult to diagnose the problem. 

The following are Billybob's comments.

Looking under the JMRI Edit menu and selecting Preferences then Connections will only report the identity of the COM port that JMRI is attempting to use.  That does not really "check" the COM port.

JMRI does not have any specific way to "check" a connection.  Usually, one can use the "Power Control" tool to (try to) turn "DCC track power" on and off.  If that control actually changes DCC track power, then the COM port is properly communicating with the DCC system.  If not, then you have one or more of any of a number of common problems.

The advice below is of a general nature.  The use of Windows "Device Manager" to check the status of the connection to the device is operating-system-specific.  Other operating systems require different methods to check operating system  connectivity status, and are not discussed here.

1) The device is no longer using the COM port it had previously used. This is VERY common for some interface devices, and entirely unlikely with other interface  devices.

• Under Windows O/S, use the Windows "Device Manager".  Check under "Ports (COM & LPT)" for your device.  If there is a problem between the operating system and your hardware, it will become evident by looking there.
• If the device is connected, the line for your device will report the COM port number currently assigned to the device.  JMRI will not "connect" to your hardware via any COM port number other than the one listed here.
• If there is some sort of a problem between the interface hardware and the operating system, it will be reported here, usually via an "exclamation-point" in yellow or red on the icon at the leading end of the line associated with your device.
• It may be necessary to load or re-load the interface device manufacturer's driver software if the operating system has chosen to replace the drivers with ones of their own.  Consult the interface device manufacturer for drivers and instructions.

2) Another common cause can because the interface device isn't really connected.

• If the interface device provides any "status" lamps or LEDs, check them carefully.  If they aren't displaying the correct status, then you need to check the hardware and its power and data connections and cables and jacks.  And consult the manual and perhaps the manufacturer.
  

3) Another somewhat-common cause is that JMRI and the connected device "think" that they are connected, but the connected device is actually "locked-up".  Certain devices are known to have this sort of problem.   When it occurs, the typical solution is:

1. Quit JMRI
2. Remove the connecting cable
3. Remove power from the connected device
4. Wait 30 seconds
5. Re-power the device
6. Re-connect the cable
7. Re-start JMRI.

4) One interface device I am familiar with is notoriously subject to connectivity problems because the wire contacts in the jack are too short to reliably make contact with the connecting plug.  Simply bending the wire contacts in the jack for stronger contact with the plug has always solved that problem for me.

5) And one (increasingly rare) problem can occur when the operating system updates its device drivers and "disables" the device.  This primarily affects "USB-to-serial" devices which have a USB connection on one side and a "RS-232"-style connection on the other side.  When such a device uses a "cloned" chip, it is subject to disabling by certain driver software versions.  There are a variety of solutions to this problem, but the most-reliable solution is to replace such a USB-to-serial device with one from a "reputable" brand-name.  If you suspect this problem, consult your interface device manufacturer.

Without knowing which hardware you are using, I cannot give better advice than the above.

Regards,
Billybob

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