ESP8266 Community Forum

- Thu Oct 11, 2018 9:21 am #78577 I'm trying to connect the TX pin of a Wemos D1 Mini during the boot phase. I am connecting it to an Adafruit CP2104. I find that when the pin is connected the device does not boot. After doing some research I found that the TX pin (GPIO1) is used for strapping to chip_test_mode during boot. If the pin is low during boot then the device goes into test mode and not normal boot. How can I accomplish having this pin connected always? Can I use a pullup resistor to hold it high and if so will this mess with the UART functionality of the pin?

Thanks,
Wes

- Thu Oct 11, 2018 5:11 pm #78585 On the Wemos GPIO01 / TX0 is already connected to the onboard USB / Serial converter (CH340C) RX Pin so that any data transmitted is accessible on the USB.

Are you trying to connect another USB serial converter in parallel with to the existing TX connection? Why?

Theoretically this could work assuming the TX output can drive both receivers without getting too loaded. You can't connect a driver externally to the RX pin as this is already being driven by the CH340C

You also have to be careful with labelling of some converters. The TX output from the ESP8266 must go to the input of the converter. Some converters are labelled with the input as RX (logical). Some are labelled with it as TX indicating that this pin should connect to the TX pin of the ESP8266. If you get it the wrong way round then you will have 2 TXs driving the same line and that will definitely cause problems.

- Thu Oct 11, 2018 5:25 pm #78586 Thanks, i suspected that might be the case.

I'm doing this because I want to power the D1 externally from the USB connection so that I can measure current draw to the device. One workaround I guess would be to breakout the USB lines so that I can remove the power.