ESP8266 Community Forum

- Tue Mar 28, 2017 1:57 pm #64343 Hi all,

I got a USB to TTL converter and am now trying to communicate to my NodeMCU board. Not entirely successful.

Connecting the board over the USB cable allows me to upload programs from the Arduino IDE just fine. No other pins connected.

Then I connected the USB to TTL converter: RX to TX and TX to RX, GND to one of the GND pins and the +5V output to Vin. The jumper is set to 3.3V for the TTL levels.

The board powers up just fine this way, and the LED starts blinking (I uploaded my Blink program over the micro-USB connection for testing). Connecting the serial monitor I get the "on" and "off" messages from the board, so receiving data over RX/TX works, showing my wiring is at least correct.

But programming doesn't work, it gives the common "no response" error message (sorry no copy/paste as I'm now on a different computer). The LEDs on the USB/TTL do flicker a bit when I try to do the upload.

What could possibly be wrong here?
Really hope to get this working so I can move on to playing with an ESP-12F module. That module gives the same errors when trying to upload, which is why I went to the known-good NodeMCU to test.

- Thu Mar 30, 2017 1:42 am #64394 In the two days it took to get this post pubilshed I finally managed to find the answer. For future reference:

To upload software / ESP-12F, start up as follows:
- RX of the board to TX of the USB/TTL device and vice versa (make sure the USB adapter is set to 3.3V).
- GND from USB/TTL device to GND of ESP8266 (the +3.3V of the USB adapter is not used).
- GPIO0 and GPIO15 to GND.
- EN and RST to 3.3V.
After uploading the sketch, the program will be run immediately.

For normal operation:
- disconnect GPIO0.
- GPIO15 must be pulled low upon start up, or the device won't start up.

- Tue Apr 04, 2017 6:14 pm #64636 what do you mean by:

- GPIO15 must be pulled low upon start up, or the device won't start up. - See more at: viewtopic.php?f=13&t=14326#sthash.yTLECwG6.dpuf

- Wed Apr 05, 2017 10:54 am #64658

what do you mean by:

- GPIO15 must be pulled low upon start up, or the device won't start up. - See more at: viewtopic.php?f=13&t=14326#sthash.yTLECwG6.dpuf

The first 250 ms or so from powering up the ESP12, GPIO15 has to be pulled low. A 10k resistor to the ground does that just fine. After that you can use the port as normal GPIO port. Leave it floating and the ESP12 won't boot.