There are two stages, one which converts RS-232 to TTL, and the other converts TTL to USB. [André] removed the RS-232 chip and patched his own board (shown on the left) into its TTL lines.

Claimed as easy to use, the E5805A USB-to-RS232 interface can connect up to four RS232 test instruments to the USB port on a personal computer at baud rates up to 230 Kb/s per serial port. No ...