Printf

• printf("%#08x\n", i); // gives 0x000007
• printf("addr:0x%x, data:0x%x\r\n", addr, flash_data); // ... 0xFF

• printf("%02X \n", (UINT16)SPIdat); // hex data // 02 表示不足两位，前面补0输出；如果超过两位，则实际输出

30 30 20 20 0D 0A 
30 30 20 20 

Purchar STM32

PUTCHAR_PROTOTYPE
{
 /* Place your implementation of fputc here */
 /* e.g. write a character to the EVAL_COM1 and Loop until the end of transmission */
 HAL_UART_Transmit(&huart1, (uint8_t *)&ch, 1, 0xFFFF);

 return ch;
}

• https://www.runoob.com/cprogramming/c-function-printf.html