On the internet there are manu links with information. N5PZR got some good information.
To make your own Serial cable you can follow this diagram.

http://www.n5zpr.com/Media/icom_cables.pdf

If you want to use D-rats you need to make your own serial cable for the E-880, E92D or 2820.

For D-Rats  on the Icom E-880 use the 2,5 mm stereo phone plug diagram the same as for the 2820. Note that there are 2 diagrams, one for connecting a GPS
and one for data-communication. The difference is that pin 2 and 3 on the DB9 connector is “crossed”. As you can see on the PDF file from N5PZR  Between the DB9 connector and your PC you can use a USB-Serial cable.

d-star-serieel