I'm trying to use a CH340G chip with an ATmega328P that is running on 3.3V to have a simple serial to USB interface. The available datasheets for this chip seem to be very minimal so I've tried finding out more in forum posts. Some links provide more information but it's not completely clear:
When comparing the usage of CH340G with the popular FTDI FT232RL one thing seems peculiar: In those user-provided example schematics the Tx pin of the CH340G is connected to the Tx pin of the ATmega328P and the Rx pin to Rx, when for FT232RL they would be crossed.
The schematic supplied by the fobit blog suggests:
Atmega328P Tx -> CH340G Tx
Atmega328P Rx -> CH340G Rx
CH340G D+ -> USB connector D+
CH340G D- -> USB connector D-
Is this correct? Even though using a 3.3V 1117 voltage regulator for VCC, wouldn't one need additional resistors on the D+ and D- to drop the USB voltage of 5V to 3.3V on these data lines as well? If so, which value has to be used as it's unclear how much current flows on the data lines? Neither the user supplied 3.3V CH340G schematic nor the datasheet mention that.
A minimal translated datasheet can be found here and some relevant info is on page 4:
A schematic for a 3.3V setup found on http://fobit.blogspot.com/2014/11/ch340g-in-eagle.html http://i.imgur.com/vUIm3SF.png
Thank you in advance.