Restore trust in the CH340 USB-Serial Interface chip

[TG9541]

Using the STM8 eForth 2-wire-interface with a CH340 based USB-Serial interface adapter never worked in a reliable way: some adapters worked, but most adapters never worked reliably (or at all). I suspected either the impedance of the device's TxD, or the low-level threshold of RxD to be too high.

While reverse-hacking a CH340G based RS485 adapter I found the simple reason for the malfunction: the designers of the most common CH340 based serial interface adapter inserted a 1k5 resistor in the TxD line (see picture). After removing that resistor (e.g. by soldering a bit of wire on top) the adapter works just as well as any other TTL-serial interface. I guess I should have removed the shrink-wrap earlier.

Thus, the CH340 has nothing to do with the malfunction, and a quite some doc locations in Wiki and elsewhere need to be updated.