JMRI: Communications Monitor Window
Author: Bob Jacobsen
Keywords: JMRI help monitor

# Communications Monitor Window

JMRI provides a communications monitor window so you can see what's happening on the communications link between the program and the layout hardware.

Once you open a monitor window, it will automatically display all traffic on the link as long as "Filter Bytes" is blank.

## Controls

Clear Screen
  Erases the log area at the top of the screen
Freeze Screen
  Stops acquiring new information, so that the captured information stops scrolling up
Show raw data
  Normally, the monitor displays the program's interpretation of what it's seeing. If you want to see the raw bytes, check this box.
Show timestamps
  Normally, the program just displays the data from the communication link. If you'd like each message to be preceded by the time it was sent or received, check this box.
Add message
  If you want to insert a message into the captured information, e.g. to make a note about what you're about to do, you can type it into the text field next to the "Add Message" button and then click that button. This is particularly useful when you're logging to a file (see below) and want to make a note for later about what's happening.
Filter Bytes
  You can filter unwanted messages from the window by entering each message's first hex value into the "Filter Bytes" field. This can be especially helpful when there is a lot of routine comm traffic. Separate multiple values by spaces. e.g. "B0 D0 CC". This example will suppress any messages whose raw data starts with "B0", "D0" or "CC" You can determine the available hex values by turning on "Show raw data."

## Logging To A File

Sometimes, it's helpful to capture what's happening. For example, you might encounter a bug (!!), and want to send a copy of what's happening to the people who are trying to fix it.

Small amounts of data can be copied from the log window with your computers "copy" command (e.g. ctrl-C or cmd-C), and then pasted into an email.

If you want to capture more, you can have the window write a log file on your computer's disk. To do this:

1. Click "Choose log file". A file-chooser window will open. Navigate to where you want to store the file, enter a name for the new log file, and click "Save". Note that if you pick a file that already exists, it will be overwritten.
2. When you're ready to capture the data you want, click "Start logging" on the monitor window.
3. When you're done, click "Stop logging" to store the data and close the file.