UART baud rate error calculator
Serial frames drop at 115200 baud and the cause is the divisor error on your clock, not the cable. Divisor register, actual baud and percentage error for 16x and 8x oversampling formats.
Open the calculator in EM·LINKBelow is a worked example. The working calculator runs free in EM·LINK.
Worked example
Example inputs
Example result
Too much for 8N1 once the other end adds its own error. Use 8x mode or change the clock.
| Mode | Divisor | Actual baud | Error |
|---|---|---|---|
| 16x | 8 | 111 111 | −3.55 % |
| 8x | 16 | 117 647 | +2.12 % |
With an 11.0592 MHz crystal the 16x divisor is 5 and the rate is exactly 115 200 (0.00 %).
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The working calculator is UART Baud Rate Error in EM·LINK, our free browser tool. The button opens it directly.
How to read the result
At 16 MHz and 115200 baud, 16x mode gives -3.55 percent error and drops frames; 8x mode gives +2.12 percent. An 11.0592 MHz crystal gives 0.00 percent, which is why that odd frequency exists.
Error accumulates over about 10 bit times per frame, and both ends contribute.
How this is calculated
The divisor must be a whole number, so the actual rate is the clock divided by the oversampling factor and the rounded divisor. The error is how far that lands from the target.
The full derivation, step by step, is in the EM·LINK documentation.
Calculated per common engineering practice (standard UART timing with 16x and 8x oversampling). These tools are an engineering aid, not a certification.
Next step
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Common questions
Why does 115200 fail on a 16 MHz MCU?
The 16x divisor gives about -3.55 percent error. Use 8x mode or a baud-friendly crystal.
How much baud error is acceptable?
Keep the combined error of both ends well under about 4 to 5 percent for 8N1.
Why 11.0592 MHz?
It divides exactly into standard baud rates.
Related tools
- RS-485 termination and bias, to rule out the line once the clock checks out.
- CRC and checksum, to check the frames that do arrive.
- Modbus register interpreter, when the link is clean and you need the values.