The TTL-232R-3V3-AJ-RP ("audio jack" with "reverse polarity") is a USB-to-Serial (3.3V TTL level) converter cable which allows for a simple way to connect TTL serial interface devices to USB. This version of FTDI's USB-to-TTL serial adapter uses a 3.5mm audio plug on the serial interface and has its I/O pins configured to operate at 3.3V levels.
The TTL-232R-3V3-AJ-RP uses an FT232RQ device which is housed inside the USB 'A' connector, and is terminated at the end of a 1.8m (70") cable with a 3.5mm audio jack which provides access to transmit (Tx), receive (Rx), and GND signals. This -RP version has the Tx and Rx lines reversed compared to the TTL-232R-3V3-AJ.
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