Common Errors When Using UART with AT91SAM9260B-CU and How to Fix Them

Common Errors When Using UART with AT91SAM9260B-CU and How to Fix Them

Sure! Here’s a detailed analysis of common errors when using UART with the AT91SAM9260B-CU microcontroller and how to fix them.

Common Errors When Using UART with AT91SAM9260B-CU and How to Fix Them

The AT91SAM9260B-CU microcontroller is equipped with a Universal Asynchronous Receiver Transmitter (UART), which is a popular interface for Communication . However, when using UART for serial communication, users may encounter various errors. These errors can stem from configuration issues, hardware problems, or software-related mistakes. Here’s an overview of common UART issues and how to troubleshoot and resolve them.

1. Incorrect Baud Rate Configuration

Cause: The baud rate is the rate at which data is transmitted over the UART. If the baud rate of the AT91SAM9260B-CU is set incorrectly, the communication will fail, leading to corrupted data or no communication at all.

How to Identify:

Mismatch in communication speeds between the microcontroller and the connected device (e.g., PC or another microcontroller). Data appears corrupted, with random characters or gibberish.

Solution:

Check the UART configuration registers to ensure the baud rate is correctly set. Compare the baud rate setting on both sides of the communication (e.g., the AT91SAM9260B-CU and the connected device). Use the formula provided in the AT91SAM9260B-CU datasheet to calculate the baud rate divisor based on the system Clock . Adjust the baud rate to match between both devices.

Example Code for Baud Rate Configuration (pseudo):

#define UART_BAUD_RATE 9600 unsigned int baud_divisor = (system_clock / (16 * UART_BAUD_RATE)) - 1; UART->BRGR = baud_divisor; // Set the baud rate register

2. Data Framing Errors

Cause: A framing error occurs when the UART receiver detects that the start or stop bits in the data frame are not in the correct position. This usually happens if the data is being transmitted at an incorrect baud rate or with incorrect parity settings.

How to Identify:

Unexpected or distorted data is received. A "Framing Error" flag may be raised in the UART status register.

Solution:

Ensure that both the sender and receiver have identical data format settings, including data length, parity, and stop bits. Common data format is 8 data bits, no parity, and 1 stop bit. Check the UART control registers to verify the data frame format is correct.

Example Code for Setting Data Format:

UART->MR = UART_MR_PAR_NO | UART_MR_CHMODE_NORMAL | UART_MR_NBSTOP_1 | UART_MR_CHRL_8; // 8N1 format (8 bits, No Parity, 1 Stop Bit)

3. Parity Errors

Cause: Parity errors occur when the parity bit does not match the expected value. This often happens if the UART is configured with the wrong parity setting or if noise corrupts the data.

How to Identify:

Parity error flags are raised in the UART status register. Corrupted or incorrect data with an extra bit that doesn’t match the expected parity value.

Solution:

Make sure both devices (AT91SAM9260B-CU and the connected device) are using the same parity settings. If no parity is required, configure UART for "No Parity." If parity is required, ensure that both even and odd parity settings match between both devices.

Example Code for Parity Setting:

UART->MR = UART_MR_PAR_EVEN; // Use even parity

4. Buffer Overflow Errors

Cause: Buffer overflow occurs when the UART receiver buffer is full and new incoming data overwrites the existing data. This typically happens if the data is being received too quickly and the software isn't reading the data fast enough.

How to Identify:

Loss of data. UART status register indicates a "Buffer Overflow" error. Missed or incomplete data packets.

Solution:

Implement proper flow control (e.g., RTS/CTS or XON/XOFF) to manage data flow. Ensure your software is reading data from the UART buffer quickly enough to prevent overflow. Increase the priority of UART interrupt handling if using interrupt-driven communication.

Example Code for Interrupt-driven UART:

// Enable UART receive interrupt UART->IER = UART_IER_RXRDY;

5. Pin Misconfiguration or Improper Connections

Cause: If the UART TX/RX pins are not correctly connected or configured, communication will fail. For instance, the TX pin might be connected to an RX pin on the wrong device, or the UART pins might be incorrectly set in the microcontroller's GPIO configuration.

How to Identify:

No communication at all or incomplete communication. A “Line Error” may appear, and there may be no data being transmitted.

Solution:

Verify the correct physical connections between the UART TX and RX pins. Ensure that the GPIO pins are correctly configured as UART TX/RX.

Example Code for Pin Configuration:

// Configure UART TX pin as output, RX pin as input PIOA->PIO_PDR = PIO_PA9; // Disable the default function of pin (TX) PIOA->PIO_ABSR = PIO_PA9_UART0_TXD; // Assign to UART function

6. Incorrect Interrupt Configuration

Cause: If the UART interrupt is not properly configured, data may not be read correctly when it's ready, leading to lost or unprocessed data.

How to Identify:

Data is not being processed as expected, even though it appears to be arriving. The interrupt flags for data ready or received might not be triggered.

Solution:

Ensure that UART interrupts are enabled for data reception. Check the interrupt enable registers to make sure that interrupts are enabled for UART events like data reception or transmission ready.

Example Code for Interrupt Configuration:

// Enable UART receive interrupt UART->IER = UART_IER_RXRDY;

7. Incorrect UART Clock Source

Cause: The AT91SAM9260B-CU uses a specific clock source for UART communication. If this clock is incorrectly configured, the UART may not function correctly.

How to Identify:

Baud rate mismatches. Communication issues similar to incorrect baud rate settings.

Solution:

Verify that the system clock is configured correctly for the UART peripheral. Check the system clock configuration and ensure that the clock source for the UART is stable.

Conclusion

When using UART with the AT91SAM9260B-CU, common issues can be traced to configuration errors, miscommunication between devices, or incorrect clock sources. Always double-check the baud rate, data format, pin connections, and interrupt configuration to ensure reliable communication. With careful troubleshooting, these issues can typically be resolved quickly.