Question

assume the baud rate transmission is 115.2 kbps . data packet consists of 8 bits data (0XAA), one bit odd parity and 1.5 bits stop along with start bit . draw the packet and determine the time that uart will take to transmit this packet ?

Answer 1

Assume baud = 115.2 kbps = 115200 bits/s. Bit time = 1/115200 = 8.680555... µs.

Frame composition:
- Idle line = 1 (mark)
- Start bit = 0 (1 bit)
- 8 data bits (0xAA = 0b10101010) — UART sends LSB first: D0..D7 = 0,1,0,1,0,1,0,1
- Parity = odd. Data has four 1s (even) so parity bit = 1 to make total ones odd (1 bit)
- Stop = 1.5 bits (high level)

Bit count = 1 (start) + 8 (data) + 1 (parity) + 1.5 (stop) = 11.5 bits

Time to transmit = 11.5 bits × (1/115200 s/bit)
= 11.5 / 115200 s
≈ 0.00009983 s ≈ 99.83 µs

Per-bit time and stop-time:
- 1 bit = 8.6806 µs
- 1.5 stop bits = 1.5 × 8.6806 µs ≈ 13.021 µs

Packet (values, LSB first):
Idle(1) | Start(0) | D0=0 | D1=1 | D2=0 | D3=1 | D4=0 | D5=1 | D6=0 | D7=1 | Parity=1 | Stop=1 (1.5 bits)

Total transmit time ≈ 99.83 µs.