I have a NodeMCU board with a broken UART module. So I tried to program the esp8266 via an external CP2102 breakout board. I have powered the NodeMCU directly with 3.3V on the 3.3V pin and connected TX/RX/GND of the CP2102 breakout board.

I am able to receive the "ets Jan 8 2013,rst cause:2, boot mode:(3,7)" via the serial monitor of the arduino ide. But I just get an error when I try to program the esp826 with the arduino ide:

warning: espcomm_sync failed error: espcomm_open failed error: espcomm_upload_mem failed error: espcomm_upload_mem failed

What I am doing wrong? I am pressing Flash, tap reset and release the flash button on the nodemcu board.


1 Answer 1


If you are powering the esp8266 directly from the 3.3v pin of the CP2102 board, this one doesn't has the enough current (>200mA) to run the esp8266. You must to connect the esp8266 to an external 3.3V power supply which should give more than 400mA.

  • \$\begingroup\$ I am using an external power source for 3.3V \$\endgroup\$
    – Schr0nk
    Mar 1, 2017 at 8:20
  • \$\begingroup\$ Which baud rate are you using it? \$\endgroup\$ Mar 13, 2017 at 1:20

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