Not always, it really depends on what the person who did the board layout or wrote the firmware thought. When I do a board/firmware I label it from the devices perspective, so the TX is where the bits I'm transmitting will be coming out of, RX is where I'm expecting your bits to be sent to. Others label it from the perspective of the device connecting to it. So TX is where you connect the line your sending bits from. To me that's wierd because, to others it's what they expect. There is no standard and the result is you end up hooking it to an oscilloscope and see which line bits are being sent from. Then you use the scope to figure out all the settings. If they don't transmit in power up then... Frustration ensures