No Start Bit in UART (nRF51822)

[Manuel Kwong]

Dear all,

I make a simple test on the UART0, putting the code in 'simple_uart.c' to my main.c. When I send out a character 'A', 0x41. From the CRO timing, it appears that the START bit is lost. Please help as the receiver MCU cannot extract the data without the START bit.

Also, although I write '0' to NRF_UART0->CONFIG, but still found 9 data bits waveform.

any clue on this are welcomed.

thanks & regards, manuel

[awneil]

What makes you say that the start bit is lost?

Can you post an oscilloscope or logic analyser plot of the signal?

Are you sure you have correctly configured the baud rate ... ?

[Manuel Kwong]

Dear awneil,

Picture is attached above, the delta t is 1.874ms and it is 9 bit data with my setting being 4800 baudrate (using the constant provided in nrf51_bitfields.h: #define UART_BAUDRATE_BAUDRATE_Baud4800 (0x0013B000UL) /*!< 4800 baud. */ it is correct setting to be 4800. My data sending out is 0x41, so the first bit '0' is data bit, not start bit but adding the 9th bit at trail. It is strange that I set the CONFIG register to be 0x00.

[Manuel Kwong]

wrong on the endian arrangement, the waveform is correct, problem solved.