Good day!

Seems like TNOW signal on CH579 is "Active 1", inverted relative to "Active 0", usually used by RS485 tranceivers. Is it true or  I am missed some settings?

You are right, the TNOW signal on ch579 is the same as that on ch340 series.

When the transfer is active, TNOW will be set to 1.

To use it ,all you have to do is just like this :

		GPIOB_SetBits(bTXD0);
		GPIOB_ModeCfg(bRXD0, GPIO_ModeIN_PU);
		GPIOB_ModeCfg(bTXD0, GPIO_ModeOut_PP_5mA);
		
		//enable TNOW
		GPIOB_ModeCfg(GPIO_Pin_5, GPIO_ModeOut_PP_5mA);
		R8_UART0_MCR |=RB_MCR_TNOW;
        R8_UART0_IER = RB_IER_TXD_EN|RB_IER_DTR_EN;
	
		UART0_DefInit();