dimension 8400 ieee 1394 question

there are two ieee 1394 six-pin sockets on the 8400 which i
assumed were two separate ieee 1394 connectors that could be
used concurrently by different devices.

i connected a movie camera to one port and an external hard
drive to the other, hoping to copy the movie tape to the
external drive. capture software was unable to operate the
camera until i switched off the external drive.

device manager shows 'ohci compliant ieee 1394 host
controller' and gives no indication of separate ports. are
these ports designed to run two devices concurrently?
--David