IBM 6400 Setup Manual page 144

Port Type
Selects the type of port to be used. The Disable selection disables the port
from the hotport process. The available selections are:
Twinax (the default)
Coax
Disable
Timeout
This is the value used by the printer to time out from the current port and
check the other ports for data to print. When the printer has not received data
from the host after the specified period of time, it needs to Timeout in order
to service the other ports. The available selections are 10 to 180 seconds. The
default is 15 seconds.
4–28 6400 Line Matrix Printers Setup Guide, Cabinet and Pedestal Models