HDTV and cable modem using same outlet - XFinity

We have been using a splitter for our digital TV and our cable modem for several years. We got an HDTV and updated our set top box to the HDTV model. Now, we have no internet unless you disconnect the TV from the set top box. Do we have to have another cable outlet installed or is their a different way to correct this problem?

This question, "HDTV and cable modem using same outlet," is about XFinity-Comcast TV television equipment.

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