[Solved] Using TXD0, RXD0 for Serial Communication on ESP8266 NodeMCU Without USB

Hello,
Is it possible to use TXD0, RXD0 for serial communication with an external circuit when USB communication is not used in the Node MCU ESP8266?

Between the output pins from the TXD0 and RXD0 board and the TXD and RXD from the CH340G there are resistors 470Ω so that theoretically it should be possible to communicate with other chips over serial0.
If the external chip is unplugged during programming there should not be a problem w/o me or am I thinking right?
I use TXD2 and TRX2 for the hardware SPI and I want to receive data in an interrupt so the hardware serial does not suit me.

Jacek Rutkowski wrote:

can TXD0, RXD0 be used for serial communication with an external circuit when USB communication is not used on the Node MCU ESP8266?

.
Generally, yes.

Jacek Rutkowski wrote:

If the external chip is unplugged during programming there should be no problem with this in/by me or am I thinking correctly?

.
As long as the CH340 is powered, a low state will be forced on its RXD/TXD pins, which will probably cause problems in communication over UART0. The CH340G is powered from 5V, so you would need to power the NodeMCU directly from 3V3 (do not use the LDO on the board) and thus depower the CH340G.

.

This is what I was afraid of but I think if I give something that provides more than 3V on these 470Ω it should work. I don't want a separate power supply because the LDO is probably reverse conducting too....

The SPX3819 regulator has an EN input - if a voltage of less than 0.4V is applied to it, the regulator will be switched off.

Unfortunately but I have this version 3 with AMS1117 and cutting off +5V is not the best idea w/ me. I'll stick with the more powerful driver and probably check later today how the communication will behave under an oscilloscope.
.

After using the LVC1G32 like a buffer on the rxd input, communication works perfectly at 115200bps