51822+uart framing+break issues

[jeremie]

Hi

for some reason I cannot connect any PC terminal to my custom board: I would get consistent NRF_UART0->ERRORSRC = 0x000c or 0x0004 indicating break and/or framing issue. I hope someone has any hints to help me out ...

Here is my setup:

• custom board, RX pin = 30, TX pin = 0, no CTS/RTS
• nrf51822 QFAAH0 + SDKv5_2_0 + SD110v6.2.1 (can't change any of those)
• SD is initialised
• app_uart is configured as follows:

const app_uart_comm_params_t comm_params =  
	    {
		DBG_RX_PIN, DBG_TX_PIN, 
		0, 0,
		APP_UART_FLOW_CONTROL_DISABLED, false,
		UART_BAUDRATE_BAUDRATE_Baud115200
	    };
	uint32_t err_code;
	APP_UART_FIFO_INIT(&comm_params, 64, 64, uart_error_handle, APP_IRQ_PRIORITY_LOW, err_code);

• uart_error_handle does the following:

void uart_error_handle(app_uart_evt_t* p_event) {
    switch (p_event->evt_type)
    {
    case APP_UART_COMMUNICATION_ERROR:
        ui_printf("ERROR %x\n", p_event->data.error_communication);
        break;

    default:
        ui_printf("OTHER\n");
        break;  
    }
}

• using USB<>Serial cable (based on PL2303), connected as follows:

nrf-tx-pin <=> rs232-pin2
nrf-rx-pin <=> rs232-pin3
nrf-gnd    <=> rs232-pin5

• using any Terminal application on Windows/Mac, e.g. screen or RealTerm, configured 115200,8N1
• whether my custom uart driver or SDK's app_uart.c, I get the same results:

Results:

1. Whenever I press a key on the terminal, I get a ERROR 0x0004 followed immediately by a ERROR 0x000c on the board, The terminal app also indicates a BREAK + ERROR
2. Changing baudrate does not help, some (e.g. 19200) even have weird consequences on display(!)
3. Changing parity does not help
4. (weird) if I disconnect GND (pin 5), the terminal app does not indicate any BREAK + ERROR error anymore but the board still does

any ideas/hints ?

[Turbo J]

You need to use a converter like MAX3232 to convert from the high voltage RS232 signals (up to +-15V!) to the UARTs 3.3 Volts on the NRF chip.

Note that the high RS232 voltages can fry the NRF chip rather quickly - never connect these directly to microcontroller pins.

[jeremie]

arggg ... rings a bell, now that you say that; for some reason I repressed this part. thanks a lot Turbo J !