Pic Baud Rate Calculator

PIC Microcontroller Baud Rate Calculator

0 – Low Speed 1 – High Speed

0 – 8-bit Timer 1 – 16-bit Timer

Calculation Results

Calculated SPBRG:

Actual Baud Rate:

Percentage Error:

Max Possible SPBRG:

⚠️ Warning: The calculated value exceeds the register capacity! Try changing BRGH or BRG16 settings.

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Understanding PIC Baud Rate Generation

When working with PIC microcontrollers (PIC16, PIC18, or PIC24/dsPIC), the Enhanced Universal Synchronous Asynchronous Receiver Transmitter (EUSART) module requires precise timing to communicate with external devices like PCs, sensors, or other MCUs via RS232/UART. The Baud Rate Generator (BRG) is a dedicated 8-bit or 16-bit timer that determines the communication speed.

The Governing Formulas

The baud rate depends on three main factors: the clock frequency (Fosc), the BRGH bit (High-Speed bit), and the BRG16 bit (16-bit Baud Rate Register bit). Depending on these settings, the formula changes:

• 8-bit / Low Speed (BRGH=0, BRG16=0): Baud = Fosc / (64 * [SPBRG + 1])
• 8-bit / High Speed (BRGH=1, BRG16=0): Baud = Fosc / (16 * [SPBRG + 1])
• 16-bit / Low Speed (BRGH=0, BRG16=1): Baud = Fosc / (16 * [SPBRG + 1])
• 16-bit / High Speed (BRGH=1, BRG16=1): Baud = Fosc / (4 * [SPBRG + 1])

Why Baud Rate Error Matters

Asynchronous communication relies on both the sender and receiver having nearly identical clocks. If the error between the desired baud rate (e.g., 9600) and the actual achieved baud rate (based on the integer value in SPBRG) is greater than 2% to 3%, data corruption is likely. This tool helps you find the configuration with the lowest possible error percentage.

Practical Example

Suppose you are using a 4 MHz crystal (Fosc) and you want a 9600 Baud Rate:

1. Using 8-bit High Speed (BRGH=1): SPBRG = (4,000,000 / (16 * 9600)) – 1 = 25.04.
2. Rounding to 25, the actual baud rate is 4,000,000 / (16 * (25+1)) = 9615.38.
3. The error is roughly 0.16%, which is excellent for stable communication.