Can you Invert the UART TX Pin

DaveTiff · March 25, 2021, 9:13pm

Hi

The UART Pin normally sits Hi, and goes low when data is sent. Can this be inverted.

If so, what is the syntax?

Regards, Dave

sender · March 26, 2021, 6:37am

I think not atm in software. But there seems to be an update coming…

DaveTiff · March 26, 2021, 9:20am

Thanks, I am using a ESP8266 so might have to do it in hardware this time.

But will keep an eye on this topic.

Thanks for the reply, Regards, Dave

jo-bru · August 30, 2022, 10:25am

Quick update:
This seems to be implemented now also for ESP8266:

github.com/esphome/esphome

Expand uart invert feature to ESP8266

esphome:dev ← Lewn:UART-invert-for-esp8266

opened 06:59PM - 26 Apr 21 UTC

Lewn

+23 -1

# What does this implement/fix? ~Expands the ``invert`` option added for the… ESP32 in #1586 to the ESP8266.~ Changes the ``invert`` option from #1586 to use the more idiomatic configuration using the full pin scheme. It also implements this feature for the ESP8266. ~As the esp8266 arduino library only implements this for UART0, a combination of ``invert`` and ``tx_pin: GPIO2`` will fall back to using software UART.~ To also support different pin combinations, a the inverting behaviour is also implemented for ``ESP8266SoftwareSerial``. ## Types of changes - [ ] Bugfix (non-breaking change which fixes an issue) - [X] New feature (non-breaking change which adds functionality) - [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected) - [X] Configuration change (this will require users to update their yaml configuration files to keep working) (on request of Otto, see below) **Related issue or feature (if applicable):** N/A **Pull request in [esphome-docs](https://github.com/esphome/esphome-docs) with documentation (if applicable):** esphome/esphome-docs#1117 # Test Environment - [ ] ESP32 - [X] ESP8266 - [ ] Windows - [ ] Mac OS - [X] Linux (Home Assistant on Home Assistant OS) - [X] ADALM2000 logic analyzer/signal generator to verify incoming and outgoing signals ## Example entry for `config.yaml`:  ```yaml # Example config.yaml uart: # UART0 - id: uart0 tx_pin: number: GPIO1 inverted: yes rx_pin: GPIO3 baud_rate: 115200 - id: not_uart1 tx_pin: # SoftwareSerial - id: sw tx_pin: GPIO5 rx_pin: number: GPIO4 inverted: yes baud_rate: 115200 ``` # Explain your changes I needed to communicate over inverted lines, and this was only supported for the ESP32, I decided to implement it for the ESP8266 for my own needs. I think it might benefit others as well. ## Checklist: - [X] The code change is tested and works locally. - [X] Tests have been added to verify that the new code works (under `tests/` folder). If user exposed functionality or configuration variables are added/changed: - [X] Documentation added/updated in [esphome-docs](https://github.com/esphome/esphome-docs).

A short check showed that it works, but I can’t get the UART RX pin to be inverted properly.
The RX idle voltage level is still on 3.3V…
Connecting TX directly to RX works, but when I use an external source I get the following voltage levels: logic 0: ~3V, logic 1: ~6V.
I’m doing these tests with a Wemos D1 mini (ESP8266).

Has anyone had the same issue?