Pin assignments
The LI-7550 pin assignments are given on the case interior label. The label also gives LED blink patterns for the LI-7550 USB port.
DB-9 connector on RS-232 serial cable
The serial cable (part number 392-10268) has a round connector that attaches to the LI-7550 and a female DB-9 connector that attaches to a computer. Note that not all pins are used for communication between the LI-7550 and a computer.