ESP8266 Community Forum

Hi,

I had the same problem and I spent two days on it.
On the beginning I used RS232 to TTL converter based on FTDI FT232RL IC via USB port. After two days it was the only one suspicious and I decided to use RS232C port which I had on my PCI card inside my PC.

I build simple RS232-TTL converter based on ST232C (or MAX232) circuit. It is working now without any problems. I flashed ESP8266 10 times with success and it works fine now. Remember to add 5V to 3.3V divider on ESP8266_RX pin for safety, but I noticed that ESP is 5V input tolerant circuit (I have no documentation, so it is better to be careful).

Explanation:
I noticed on my oscilloscope that transfer is organized in 1024 bytes packets and after each packet EPS8266 sends acknowledge to the PC. I noticed that after 30..33 packets ESP8266 did not acknowledged received packet and flashing procedure crashed. Probably FT232RL lost some bytes.

Best Regards
Maciej

Seems to me the problem is the cheap knock-off FTDI chips, my firmware burn was failing at various spots between 40% and 60%. Then I wired up another FTDI USB serial adapter I happen to have and it went all the was through the burn on the first try.

Strangely (to me anyway) the ESP-12 I have needs GPIO0 high and GPIO15 low for normal operating mode. More, RST doesn't need to be high (as I had read that it did somewhere.)

Had a similar issue (uploading firmware using esptool would fail during N%). My solution was to replace serial module used to communicate with the board (201). Replacing FTDI232 based module with PL2303MDL resulted in successful firmware flashing.

I had this issue as well; "Invalid Head of Packet". Instead of switching the programmer from an FT232RL, I was able to use GPIO2 as TX and left TX floating (ESP-01).