If the remote to your Vizio TV is a universal type that can control other devices, then there are codes provided for "Comcast" in the "Cable" section (Page 25) of the Vizio Universal Remote Codes document: »
store.vizio.com/document ··· odes.pdfOne of the codes listed there (0533, 0543, 0511) may be the one for Comcast DTAs.
Vizio also sells universal remotes if yours isn't one: »
store.vizio.com/accessor ··· tes.html