Yes, the 20-047 is “basically a USB to RS232 to TTL device”. The main chip is an FTDI FT232BL that does the USB to RS232 part.
As to the stereo plug pinout, I am pretty sure that the Radio Shack/GRE version follows the same pinout that FTDI uses on their complete USB to TTL cables such as the TTL-232R-AJ shown below for full-duplex mode. For half-duplex, the tip serves for both tx and rx.
Last edited by Evert; 05-07-2009 at 8:26 AM..