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Questions relating to designing PCBs
By zacharyl
#168450
So I am currently using the MSP430G2553 on my board layout in Eagle. For my application, I want to use an external oscillator. According to TI, I need to provide the mounting area of the oscillator with an "isolated ground" or a "ground island" so as to protect the oscillator from any unwanted signals/current that can be going through the main ground. This island is then connected by a short trace to the analog ground of the MSP430, this is the only attachment to the main ground of the rest of the board. My attempt at achieving this has been as follows:

1. Make a polygon around the oscillator (my ground "island")
2. Edit the properties of the island to have a rank of 1 and an isolation of 0.01 (main ground plain has rank of 2)
3. Rename the island to ground (GND), which is the same name as main ground

Whenever I do this, however, the island will merge with main ground when I click on ratsnest. Is there any way that I can get Eagle to supply me with a ground island that will be isolated from main ground? Is it absolutely necessary to have this isolated ground for the crystal?

Thanks for your time and help.