STM32F030R8配AD3485 RS485半双工自触发中断致停发故障问询

Hey there, let's break down your RS485 issue with STM32F030R8 and AD3485. This is a super common gotcha with half-duplex RS485 when interrupts are involved, so let's walk through the fixes step by step:

The AD3485 is a half-duplex transceiver—when you send data, if the receiver pin (RO) is still active (your DE/RE pin is high for transmission), it will detect the same bytes you're sending out. This triggers the USART's RXNE (Receive Not Empty) interrupt, which if unhandled correctly, will lock up your program and halt subsequent transmissions.

Yes, you absolutely need to clear the corresponding interrupt flags in your ISR—this is the most likely culprit here:

• RXNE Flag: When the RX interrupt fires, reading the USART data register (USART_DR) automatically clears this flag. If you don't read it (or explicitly clear it with USART_ClearITPendingBit()), the interrupt will keep triggering in an infinite loop, blocking all other code.
• TC (Transmission Complete) Flag: If you're using transmission complete interrupts to toggle the DE/RE pin, you must clear this flag too. Failing to do so will cause the TC interrupt to re-fire immediately, messing up your DE/RE timing.

Here's a corrected ISR example that handles both flags and filters self-sent bytes:

void USART1_IRQHandler(void)
{
    // Handle RX interrupt
    if(USART_GetITStatus(USART1, USART_IT_RXNE) != RESET)
    {
        uint8_t received_byte = USART_ReceiveData(USART1); // Reads DR, clears RXNE
        
        // Check if we're currently in transmit mode (DE/RE is high)
        if(GPIO_ReadInputDataBit(GPIOA, GPIO_Pin_4) == SET) // Adjust pin to your DE/RE GPIO
        {
            // This is our own transmitted byte—discard it and exit
            return;
        }
        else
        {
            // Process valid received data here
            // ...
        }
    }

    // Handle Transmission Complete interrupt
    if(USART_GetITStatus(USART1, USART_IT_TC) != RESET)
    {
        // Switch back to receive mode by pulling DE/RE low
        GPIO_ResetBits(GPIOA, GPIO_Pin_4);
        // Clear the TC flag explicitly
        USART_ClearITPendingBit(USART1, USART_IT_TC);
    }
}

Double-check these steps in your initialization code—missing any can lead to interrupt chaos:

• DE/RE Pin Configuration: Ensure this pin is set as a push-pull output, initialized to LOW (receive mode) at startup. This is critical for half-duplex operation.
• USART Interrupt Configuration: Only enable the interrupts you actually need. If you don't need RX interrupts during transmission, you can temporarily disable them before sending data, then re-enable after TC.
• USART Mode Matching: Confirm your USART settings (baud rate, data bits, stop bits, parity) exactly match the AD3485's configuration. Mismatched settings can cause false interrupt triggers.

You have two solid approaches to eliminate this self-trigger issue:

1. Temporarily Disable RX Interrupt During Transmission:
   • Before setting DE/RE high and sending data, disable the RXNE interrupt with USART_ITConfig(USART1, USART_IT_RXNE, DISABLE);
   • Re-enable it in the TC interrupt handler after switching back to receive mode.
2. Filter Self-Sent Bytes in the ISR:
   • As shown in the code example above, check the DE/RE pin state in the RX ISR. If it's high (transmit mode), discard the received byte immediately. This is simpler if you need RX interrupts active at all times.

内容的提问来源于stack exchange，提问作者user1575095