The following commands can be very useful for debugging DMC code on any of the current generation Galil motion controllers

TC1 - This reports back any errors that have occurred with the program

_ED - This operand will report back the last line number to have an error

SC - This is the stop code. It reports back why motion has stopped

_XQ - This operand reports back the current line that is executing, or a -1 if the program has stopped.

TR - This command turns on and off the trace feature. The trace feature reports back every command the controller executes as it is executed. (Useful for seeing the last command executed before the program haults)

Lastly, the DMCSmartTerminal software has a built in debugger feature that allows you to step through code using break points.