Returning to packet after many years away, will soon have a new radio for VHF/UHF packet. The radio, a Yaesu VX-8DR, includes an AX.25 TNC, yet the specifications and manual only refer to this built-in TNC as a dedicated APRS device. Why can't it also be used with an external input, in the case of packet transceive that is not APRS-related, such that I wouldn't need to use an external TNC between my laptop and the radio? Thanks in advance for any help.

Rob KB6CUN