ESP-WROOM-02 is not responding to AT commands as expected with AT Firm v2.2.1.0

[bmalbusca]

I using the ESP-WROOM-02 (esp8266 core) as WIFI module and the samd21g18 as main processing unit. To test, I´m using the ESP-WROOM-02 DEV board kitc and an Arduino nano IOT which has also a samd21g18 MCU. I flashed the ESP-WROOM-02 via the ESP flash download tool with the AT Firmware v2.2.1.0 . The user guide highlights that the default ESP8266 RTOS AT firmware for ESP-WROOM-02 swaps RX/TX with CTS/RTS.

For testing the UART, I used the Arduino Serial monitor and the UART connected to the on-board FTDI. To link the new pins (IO15 and IO13) , I connected the pin RX0 to IO13 and the TX to IO15 as a bypass.
When I sent any AT command (or any thing that I wrote on serial) the ESP always returned an empty line and a new line saying ready. Fist I tough that was the CR and line ending, I tried all combinations a didn´t worked.

To understand was happening I connected a logic analyser to RX0 in order to check if was the same as what I was sending via serial monitor. And it was sending right.

Then, I connected the logic to the IO15 (ESP TX). But something appeared wrong. The first message is missing a bit.