UART: How to calculate bit time?

Question

Reading this application note about timing for enable RS485 transeiver, I read that I need to ensure a time called "bit time", which depends on the baud rate, for example the document shows an example:

using 230400 baud rate the bit rate is 4.34 µs, but the document doesn't specify how to calculate this value

How can I calculate it?

The application note is here: https://www.st.com/resource/en/application_note/cd00249778-managing-the-driver-enable-signal-for-rs485-and-iolink-communications-with-the-stm32s-usart-stmicroelectronics.pdf

Answer 1

using 230400 baud rate the \$\color{red}{\text{bit rate}}\$ is 4.34 µs, but the document doesn't specify how to calculate this value. How can I calculate it?

I'm assuming that you don't actually mean \$\color{red}{\text{bit rate}}\$ - you mean the time duration for each bit.

So, take the reciprocal of the baud rate to get the time for each bit.

In other words, if you are receiving or transmitting 230400 bits per second then each bit must last 4.34027778 μs.

Answer 2

It is calculated as 1/230400 = 4.34 microseconds.

If there is X bits per 1 second, then 1 second is divided to X parts to get time of one bit.