From Wikipedia's article:
The host includes 15 kΩ pull-down resistors on each data line. When no device is connected, this pulls both data lines low into the so-called "single-ended zero" state (SE0 in the USB documentation), and indicates a reset or disconnected connection.
A USB device pulls one of the data lines high with a 1.5 kΩ resistor. This overpowers one of the pull-down resistors in the host and leaves the data lines in an idle state called "J". For USB 1.x, the choice of data line indicates of what signal rates the device is capable; full-bandwidth devices pull D+ high, while low-bandwidth devices pull D− high.
Also USB goes between smart IC's for handshaking, bit rate control, data packetizing absent on RS232 uarts.
Reproduce what a PC does when recognizing a Neato and opening a com session.
Unless Neato Shut-Down, USB detects attached devices without powering control panel on.