EAGLE hints & tricks
Today:
Never ending DRC error message list with off grid elements.
There are components on the market which never fit into any grid size using Eagle, e.g. a SUB-D-connector.
The pitch distance of those is 2.77mm and just placing an unconnected SUB-D-25 connector on a board without any signal wire will cause a list of exactly 100 errors, all resulting from "OFF GRID" elements.
This problem can be solved by disabling "OFF GRID" check during the DRC. If all 25 pins of the connector are connected somewhere the DRC will display at least 25 "ANGLE" errors, regardles of manual or autorouting. If the routing grid was not fine enough there will be addional error messages concerning "OVERLAP".
Here is a way to neatly connect a SUB-D-25 connector (male) and running a DRC with zero errors with "OFF GRID" check disabled: (You know that the device is OFF GRID!)
Route a trace with your usual grid size setting until shortly before a pin of the connector. Drop the trace and switch to grid size 1mil. Pick up the interrupted trace and while continuing routing observe the air wire which should be an undestorted straight line even at a 45 degrees angle. Connect the trace to the pin for an audible "PING".
That way traces can be routed exactly in the middle between two pins with a distance from trace center to pin center of 1.385mm.
Attached is part of a XILINX CPLD and FGPA programming adapter with the DRC displaying "NO ERRORS".
Just in case somebody is in need of the complete adapter the schematic and layout are packed in the attachment.
Boncuk