UART Waveform

Try this

1. Bits leave the sending MCU and travel along the yellow wire to the receiver. Bright yellow is HIGH (1); dark blue is LOW (0).
2. The line rests HIGH. The moment the START bit pulls it LOW, the receiver knows a frame has begun.
3. Data bits go out b0 first, least significant bit first. Compare the "LSB first" line on the sender's screen with the order on the wire.
4. Set parity to even and press Send: a P bit is added at the end of the frame.
5. Change the baud rate and the bit time and frame time below change. At 115200 bps one character passes in about 87 µs.

How to read it

The line idles HIGH. The fall to LOW is the start bit, and the receiver uses that falling edge as its reference to sample each bit in the middle. The final stop bit is HIGH again, which lets the next start bit be recognised.