Complex sentence: In the other, "command mode", data sent from the computer was instead interpreted as commands, which could be interpreted by the modem to do various operations, like hang up the phone or dial a number.
Split into simpler sentences: In the other, "command mode", data forwarded from the computer was instead interpreted as commands. In this way, the modem could be instructed by the computer to perform various operations, such as hang up the phone or dial a number.