(1) I agree eBay is not always evil, but I think eBay's quality control is not as good as Amazon or AliExpress. Actually I was once a member of AliBaBa, but I later opened an account in AliPay and TaoBao, which belongs to Alibaba. (2) I think I understand what your C++ code is trying to do, but I think it is tedious.

(3) I read the BusLink doc saying that its UART connector can be used by MCU to talk to servo, but I am not sure if you must use Win10 and install driver for that.

(4) I found Win10 RealTerm hard to handle, and I need to reset every now and then. Now I have decided to switch to Rpi4B CutCom which is simpler than RealTerm, and CuteCom is easier to convert to Thonny python. But I have only 50% confidence that my TXS0102/04 can replace the BusLink. Will take me a couple more days to find out. Cheers.

Just now I googled and find a python library for BusLink Terminal on Python. In other words no more using Windows. If your HC126 adapter is almost identical to BusLink Terminal, perhaps you can also try this python LeWanSoul LX-16A library. For now I will still carry on my TXS0104 setup.

I managed to do the C++ code, but unfortunately, I can't manage to reliably disable TX on time. The problem is that the OS timers and scheduling is on the 10ms range, while this communication happens in the 0.1ms.. This makes impossible to control enTX and TX by software on any modern OS.

If you test it, you will see that the enTX will be disabled after last bit of the UART, but with significant Jiter