To use the DCDM, plug it into the diagnostics connector on the Repeater or Upstream Termination Network (UTN) module. The three red LEDs on the right hand side of the DCDM front panel will illuminate at this point. The LCD will display "DCDM v1.2" briefly before changing to a screen that reads "UPSTREAM: xxxxxxxx" on the top line and "DOWNSTREAM: xxxxxxxxx" on the bottom line. If this configuration is correct, press start, if not, change the toggle switches until the messages on the LCD match the configuration of devices on the DART lines. The left toggle switch selects the downstream device and the right toggle switch selects the upstream device.
To use the DCDM in conjunction with a logic analyzer, simply connect the analyzer pods to the DCDM’s headers, which are described in detail in APPENDIX B. These headers provide access to the DART differential signals as well as microcontroller data and control lines.
If the DCDM is being used to test the terminations and lines, FIRST MAKE SURE THE CABLES ARE IDLE. That is, make sure that no data is being transmitted. If line signals are being asserted the DCDM will report false errors!!!
At this point the LCD should read "UPSTREAM: xxxxxxxx" on the top line and "DOWNSTREAM: xxxxxxxxx" on the bottom line. If it does not, press RESET and wait about 2 seconds.
Set the configuration toggle switches until the configuration on the screen matches the configuration of the devices on the DART cable. The press the START button to begin testing the lines. The screen should blank for a few seconds and then a message with the form "xx errors found" will appear. Pressing the start button will scroll through the individual line errors. After the last error message is displayed, "done" is printed and the DCDM will need to be reset. Refer to section 2.3 for instructions on how to interpret individual error messages.
The configuration toggles are used to describe the configuration of devices on the DART cable. The toggle switch on the left has three positions, and specifies what device is on the DOWNSTREAM side of the device the DCDM is plugged into. The toggle switch on the right has two positions, and specifies what type of device is UPSTREAM of the device the DCDM is plugged into. Start and Reset are momentary pushbuttons. On the right hand side of the front panel there are 3 red LEDS that display the status of the 3 power supplies that the DCDM uses. From top to bottom they are: VEE (-5V), Bias Power (+3.3V), and VCC (+5V).
The DCDM can test 6 separate configurations, as shown in the table below:
The DCDM displays line errors one line a time. The name of the faulty line is displayed on the top line, and the error message is displayed on the bottom line. Pressing the start button displays the next line error. When there are no more errors to display, "done." is printed and the DCDM will need to be reset.
Below is a table listing possible error messages.
RT, RM, and RB refer to a terminated model shown below. The DCDM is able to detect if any of these three resistors values are too low or too high. When the DCDM reports that a resistor is too high, most likely the specified resistor is open. Likewise, a "resistor too low" error message usually means that the specified resistor is shorted.
Although the DCDM can detect a majority of errors on the DART cables, a correct diagnosis is not always displayed. This results from the fact that the error detection algorithms needed to be general enough to apply to all configurations. Refer to section 4.6 DCDM limitations for more information.