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LPC812MAX with ESP8266 using UART

Question asked by Donald Ngai on Jul 31, 2017
Latest reply on Aug 2, 2017 by Kerry Zhou

Hi There!


I'm looking for some help with interfacing my LPC812MAX board with the ESP8266 wifi module using UART. I've tested as much as I could but now I am stumped why the devices are acting the way they are. Here were my findings:


  1. I confirmed that the ESP8266 module is working and responding correctly. I confirmed this by connecting it directly to my computer using a TTL UART cable. With this, I was able to open up a serial communication channel and broadcast the command "AT" to the wifi module. It responded "OK" at a baud rate of 115200. Confirming both the baud rate as well as the functionality of the module.
  2. Using the output of serial session, I have confirmed the exact message (including line endings) that the ESP8266 module received in order to reply with "OK". "AT<CR><LF><CR><LF>.

  3. Next, I confirmed that my LPC812MAX board is sending that exact same message by connecting it to my laptop using the TTL UART cable. With this, I confirmed that the LPC812MAX board is communicating at a 115200 baud rate and sends exactly "AT<CR><LF><CR>LF>.

The problem now is when I directly connect the ESP8266 to the LPC812MAX. Despite confirming the buad rate and the correct messages being sent, the ESP8266 does not respond. It only echoes back whatever I send to it.


Another interesting thing I noticed was that the ESP8266 might not initialize properly upon startup when connected directly to the LPC812MAX board. The reasoning behind this thought is because on startup, the ESP8266 sends over UART some gibberish followed by "READY". I can confirm this when connecting the ESP8266 to my computer. But this "READY" message is not received by the LPC812MAX board when I output everything it receives over it's UART bus. Am I missing some hardware necessary for the UART communication?

Any help would be appreciated! Thanks!