Essential type of the left hand operand usart[0U].tx_count
(unsigned) is not the same as that of the right operand "0" (signed).
if(usart[RS485_PORT].tx_count == 0) // error in this line
See Question&Answers more detail:
os 与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…