Does Serial TX have a built-in pullup resistor?

Hi - I am trying to use Serial1 on the Wiring board to talk to two Gamoto motor controller boards. Serial1 is essnetialy the same as Serial on the Arduino. I have both Gamoto boards wired in parallel as per their docs and I seem to be able to address both motors (they have a DIP switch to set board IDs) but I am getting some odd/bad data.

What I don't know is if I need the 10k pull up resistor they describe below. I tried it and it seemed to kill all communication - but maybe I hooked it up wrong. Before I assume I don't need it I thought I would ask here - does the Serial/Serial1 TX line float when not in use?

--Roy

This option is normally disabled. It allows you to connect up to 8 Gamotos to the same
serial TX and RX lines, with no additional hardware other than a 10K pull-up resistor, which may be needed in some cases. When this bit is set, the Gamoto allows the TX line to float when it's not being used. Since each Gamoto only replies to messages addressed to it (by the correct header/DIP switch combination), then only the proper Gamoto will reply. Since the TX line is floating when not in use, a 10K pull-up resistor is recommend, if not already included in your serial transceiver or MCU.