Hi,
I'm not sure which of the two connectors is the upper one, but there are two connections. One of them uses an RS-232 cable connection and the other is just a 4 wire RS-485 terminal block connector. The latter of the two has a pinout shown here in this article. Here is another useful article that addresses setting up your chassis. I hope this helps.
Chris W
Message Edited by Chris W. on 02-12-2009 04:52 PM