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How does this circuit work?

Where VDD = 5 V (MCU) and VDD_1V8 = 1.8 V.

It is a recommended circuit to use UART communication when the voltage level are not the same, I think.

enter image description here

Null
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asterix
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  • There's a large amount of text about this, and a lot of questions about level conversions here on EE.SE. What is it you don't understand about what is already explained? – pipe May 13 '19 at 15:14
  • thanks for your help, you dont even provide the link where to read. I am not living inside a forum. Pls moderator, remove this question, my post. thx – asterix May 13 '19 at 15:17
  • You may not live inside a forum but every forum has a search function. Note that the wording for the downvote button is _"This question does not show any research effort"_. – pipe May 13 '19 at 15:19
  • Okay I give you the point, I had to take some minutes the search the level matching circuit. I'm sorry. BUT you first answer is not kindly. I am asking here because I think some person of a good heart can write a short explanation about how it works. I dont mind the downvote button, I am not living of upvote or downvote button, I only am searching for a short help like TimWescott answered. Y disculpa mi tan malo inglés – asterix May 13 '19 at 15:37
  • @asterix Also see some discussion [here](https://electronics.stackexchange.com/a/297092/38098). – jonk May 13 '19 at 18:27
  • Woow they are the master of electronic. Finally I simulate the circuit I posted... Works like a charm I think – asterix May 14 '19 at 13:26

1 Answers1

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In either direction:

  • With TXD high, the emitter is pulled to or above the base supply voltage and the transistor turns off. This allows the collector/RXD junction to be pulled high by a resistor.
  • With TXD low, the emitter is pulled below the base supply voltage. Current flows into the base, the transistor turns on, and the collector is pulled down to around 0.2V.
TimWescott
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  • Thanks a lot I understand now, you are a great person!. I think I can add to my pcb the circuit without doubts – asterix May 13 '19 at 15:25