UART Baud Rate Calculator
Understanding UART Baud Rate Calculation
Universal Asynchronous Receiver/Transmitter (UART) is a hardware communication protocol used for serial communication between microcontrollers, computers, and other devices. The baud rate is a crucial parameter that defines the speed of this communication. It represents the number of signal or symbol changes that occur per second. For digital communication, one baud is equivalent to one bit per second if there is only one unique state for each symbol.
Accurate baud rate calculation is essential for establishing reliable communication. If the baud rates of the transmitting and receiving devices do not match, or if they have a significant difference (a common tolerance is around 2-5%), data corruption will occur, leading to failed communication.
The baud rate is typically determined by the system's oscillator frequency and a prescaler value. The formula used in many microcontroller UARTs is derived from dividing the oscillator frequency by a factor that generates the desired baud rate.
The general idea behind calculating the baud rate is to determine the appropriate divisor for the oscillator frequency to achieve the target baud rate. Many UARTs have a control register that allows for setting a baud rate divisor. The calculation often involves:
Baud Rate = Oscillator Frequency / (16 * Divisor) (for standard UARTs where 16x oversampling is used)
However, a more direct approach for calculating what the system *should* be configured to, given an oscillator frequency and a desired baud rate, involves finding the closest achievable baud rate. This calculator helps you determine the required divisor or provides an estimate of the achievable baud rate if a direct calculation isn't perfect.
This calculator takes your system's main oscillator frequency and the desired baud rate, then calculates the prescaler or divisor value that should be programmed into the UART's baud rate generation register. It also shows the actual resulting baud rate based on the calculated divisor, allowing you to check the error.
Example Calculation:
Let's say your microcontroller's crystal oscillator is running at 11.0592 MHz (11059200 Hz) and you want to communicate at a standard baud rate of 9600 bps.
Using the formula (and assuming a common 16x oversampling configuration, where the UART peripheral divides the clock by 16 before calculating the bit period):
Divisor = Oscillator Frequency / (16 * Desired Baud Rate)
Divisor = 11059200 / (16 * 9600)
Divisor = 11059200 / 153600
Divisor = 72
In this case, the divisor is an integer (72). This means a perfect 9600 baud rate can be achieved. You would program the UART registers with a divisor of 72.
If the division does not result in an integer, the resulting baud rate will have a small error. This calculator will show you the closest achievable baud rate and the error percentage.