UART Baud Rate Error

Formula

Description

UART communication relies on both transmitter and receiver operating at the same baud rate within a tight tolerance. The baud rate error percentage quantifies how far the actual baud rate deviates from the target. Most UART peripherals derive their baud rate from a system clock using integer dividers, which often cannot produce the exact target frequency. Errors below 2% are generally acceptable for 8-bit frames, while errors above 3-5% typically cause framing errors and data corruption.

Variables

• Error% — Percentage deviation from target baud rate
• Actual — The baud rate actually achieved by the hardware (baud)
• Target — The desired baud rate (baud)

Practical Notes

Common baud rates (9600, 115200, etc.) may not divide evenly from typical crystal frequencies. For example, a 16 MHz clock with a divide-by-16 UART achieves 115200 baud with 2.1% error. Using a 14.7456 MHz crystal gives exact division for all standard baud rates.