trying to transmit data via USART1 of STM32L476 Nucleo evaluation board. Use PA9 for TxD.
Character count is 254*2+14 = 522 or 255*2+14 = 524.
522 always is ok, 524 gives errors at receiver site.
Data switches between 'all 0x00' and 'all 0xFF' every cycle.
Use HAL_UART_Transmit (...) for sending data.
Receiver always flags Error on 0xFF packets.
Took measurement on TxD with oscilloscope. That shows that with 'all 0xFF' always 8 characters are not sent!!! (s. attachement).
What may be the cause of this?
By the way: Took a look into HAL_UART_Transmit () source code.
Found that writing TDR does not check TXE flag first (but that is not the cause of the 8 byte error).