The baud rate of a UART (Universal Asynchronous Receiver/Transmitter) defines the speed at which data is transmitted. It's measured in bits per second (bps). To achieve a specific baud rate, the UART hardware uses a clock signal and a divider value. The formula for calculating the baud rate is:
Baud Rate = System Clock Frequency / Divider
In practice, the divider is typically an integer value. This means the calculated baud rate might not perfectly match the desired baud rate. The goal is to find an integer divider that results in the closest possible baud rate to the desired one, while keeping the error percentage within acceptable limits (often around 2-5%).
How this calculator works:
System Clock Frequency (Hz): This is the frequency of the main clock provided to the UART module. Common values include 16 MHz, 11.0592 MHz, etc.
Desired Baud Rate (bps): This is the target speed for your serial communication. Common baud rates are 9600, 19200, 38400, 57600, 115200 bps.
Divider Calculation: The calculator first determines the ideal (floating-point) divider by dividing the system clock frequency by the desired baud rate.
Integer Divider: It then rounds this ideal divider to the nearest integer.
Actual Baud Rate: Using the integer divider, the actual achievable baud rate is calculated.
Error Percentage: Finally, the percentage difference between the desired baud rate and the actual baud rate is computed to show how accurate the communication will be.
A lower error percentage indicates more precise timing and a higher likelihood of successful serial communication between devices.
function calculateBaudRate() {
var systemClock = parseFloat(document.getElementById("systemClock").value);
var desiredBaudRate = parseFloat(document.getElementById("desiredBaudRate").value);
var dividerValueElement = document.getElementById("dividerValue");
var actualBaudRateElement = document.getElementById("actualBaudRate");
var errorPercentageElement = document.getElementById("errorPercentage");
// Clear previous results
dividerValueElement.textContent = "";
actualBaudRateElement.textContent = "";
errorPercentageElement.textContent = "";
if (isNaN(systemClock) || isNaN(desiredBaudRate) || systemClock <= 0 || desiredBaudRate <= 0) {
alert("Please enter valid positive numbers for System Clock and Desired Baud Rate.");
return;
}
// Calculate the ideal floating-point divider
var idealDivider = systemClock / desiredBaudRate;
// Round to the nearest integer for the actual divider
var integerDivider = Math.round(idealDivider);
// Ensure integerDivider is not zero
if (integerDivider === 0) {
alert("System Clock Frequency is too low for the Desired Baud Rate. Cannot calculate a valid divider.");
return;
}
// Calculate the actual baud rate with the integer divider
var actualBaudRate = systemClock / integerDivider;
// Calculate the error percentage
var errorPercentage = Math.abs(((actualBaudRate – desiredBaudRate) / desiredBaudRate) * 100);
// Display the results
dividerValueElement.textContent = integerDivider;
actualBaudRateElement.textContent = actualBaudRate.toFixed(2); // Display with 2 decimal places
errorPercentageElement.textContent = errorPercentage.toFixed(2); // Display with 2 decimal places
}
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