The JTAG pins are not enabled by default, they are assigned to the USB JTAG port. To use them you need to burn an eFuse (which you do via the serial port or the USB port).
To enable the JTAG pin see here.
We benefit hugely from resources on the web so we decided we should try and give back some of our knowledge and resources to the community by opening up many of our company’s internal notes and libraries through mini sites like this. We hope you find the site helpful.
Please feel free to comment if you can add help to this page or point out issues and solutions you have found, but please note that we do not provide support on this site. If you need help with a problem please use one of the many online forums.