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.

Some of the original serial interfaces like RS-232 and RS-485 are still widely used. ... Various converters are available to convert USB to TIA-232 or TIA-485, TIA-232 to TIA 485, ...