Electronic – FTDI USB/TTL-serial converter – what are TXD, TXL, RXD and RXL

I also came here because my standalone, bootloaded ATmega328 didn't want to load my program and gave that avrdude error. I solved my situation, and would like to share it so maybe it will help others.

What eventually turned out to be the issue was that the ATmega328 chip was not properly 'clicked' in the breadboard. However, when I initially placed the ATmega chip on the breadboard directly, it made a 'click' sound. It really seemed like it was in properly, not loose, couldn't go any deeper, wouldn't fall out when you shake it upside down etc. But when I tried loading a program, I got the avrdude message.

While uploading some pins were flashing, even the LED I hooked up to the pin 19 (pin 13 on Arduino board). I bought the breadboard in the Netherlands, so I can't say if it is Chinese or not, but apparently it also has some deep connectors and difficulty connecting with the pins of DIP chips. Luckily I had a chip socket mount (IC Socket 28 Pin DIP) which I placed between ATmega chip and breadboard. My problem was immediately solved, and the happiness returned.

I used a FTDI basic to program it, almost exactly just like the picture in the link of Gwideman gave above. Only the pull-up resistor of the RESET is falsely connected in that picture. Like Gwideman correctly stipulates, the resistor needs to go to pin 1, and not to the DTR-side of the cap.

In the Arduino IDE I have the 'Arduino Uno' selected.

Hope it helps somebody.

Almost certainly you are measuring your Tx line wrong. If you take a look at the data sheet http://www.seeedstudio.com/wiki/images/7/7c/CH340DS1_EN.PDF Table 6.2 says that you should be seeing ~3 volts. A break command does not normally send a DC level - it sends a logical level for 1 or more character transmit times. So your multimeter is looking at a fairly narrow pulse and averaging it.

As a quick check, try sending a continuous stream of 00 data. This should (assuming 1 start, 1 stop, no parity) give you a DMM reading of ~80% of the actual high voltage.