Pin 1 is the left-hand pin and marked on the NSLU2 PCB.
NB: In the photo above, a set of header pins has been attached to J2. As sold, J2 consists only of a series of solder filled holes in the PCB. If you wish to put a header on then you must remove the solder first.
By default, both RedBoot and the Linux kernel use 115200,8,N,1 settings.
See HowTo.AddASerialPort for details on adding a serial converter to allow usage of the serial port.
There is a second serial port on the NSLU2 but only receive and CTS are connected. It is not possible to connect to the transmit line. The connection points are on the back of the NSLU2 PCB.
NOTE: If a longer open-ended cable is connected to RxD? your NSLU maybe won't boot! Check, that RxD? gets a proper signal at least at boot-time (every time, for example, a gps-receiver isn't connected to the soldered-on RxD2?-cable, it hangs somewhere during redboot-init. This was at least observed with two different NSLU2 boxes).
A useful connection (eg, for data logging) using just RXD above and a suitable ground. I soldered wires to R128 and the shield of the existing ethernet port, and am now satisfactorily receiving data from my electricity-usage monitoring device. [http://groups.yahoo.com/group/nslu2-linux/message/488]