I'll now drive this thread off into the weeds regarding an obscure issue
with some older CP2102 USB-to-UART modules.
Most people won't care.
While verifying how the CP2102? USB-to-UART converters work, I ran into this post
? ??
where the second to the last post says:
PBudmark? ? Replied Jul 08 2017, 12:37 PM
There is a major design flaw in the board, RST-pin (9) is connected to 5.0V (VBUS).
This is reported deep into a forum on Banggood but not properly informed to buyers.
Quote: The problem with the 3.3V line at 4.2 is due to the RST input being tied not to 3.3 V out but to the Vbus in (5V) this back feeds into the 3.3V line pulling it up above spec, cut the trace you see coming from pin 9 before it reaches the capacitor, then optionally pull it to 3.3 via a 4k7 resistor to pin 6. This also seems to solve the variability with Win10? ? ?Posted 2017-02-22 09:12:56 by instoned @t aol dot com
?
The post includes a photo, showing that pins 8 and 9 of his CP2102 chip got shorted together.
From the diagram at the bottom of the first page of the CP2102 datasheet
? ??
you can see that pin8 is 5v coming in from the USB host computer.
Pin 9 is the RST (reset) pin of the CP2102 chip, and should be pulled high to 3.3v through a pullup resistor.
The CP2102 modules I got from oddwires.com? a few years ago do not have this flaw.
My modules do not have a ceramic cap placed near pins 8,9 of the CP2102 as in the above post,
the appearance of my module is significantly different.
The current CP2102 modules available from Banggood are different than the post above or mine:
? ??https://www.banggood.com/Wholesale-USB-To-TTL-COM-Converter-Module-buildin-In-CP2102-New-p-27989.html?akmClientCountry=America&cur_warehouse=CN
Oddwires now pictures yet a fourth build, with the CP2012 chip placed at a diagonal:
? ??https://www.oddwires.com/cp2102-serial-adapter-module-usb-to-rs232-with-jumper-wires/
So hopefully, the incorrect CP2102 modules are now long gone from the supply chain.
I'd go with the Oddwires product, as it has access to some additional signals (CTS, RTS, DSR, ...)
along the sides of the board.
It seems the incorrectly built CP2102 modules worked, though having Vdd up at 4.3v
is stressing the CP2102.chip.? And if driving a 3.3v processor with a 4.3v TXD,
you might be slightly stressing that processor as well.
Since our Nano has 5v IO, I doubt anything catastrophic would occur other than having?
the CP2102 module possibly fail.
Jerry
On Mon, Feb 11, 2019 at 11:42 AM, Jerry Gaffke wrote:
How to do it is documented at the bottom of this post:
? ??/g/BITX20/message/50027
In that write-up, I mention tying the 5v pin from the CP2102 to the 5v pin of the Raduino,
only do that if you want to power the Raduino from the host's USB port.
In your case where you have the Raduino installed in the uBitx, do not connect
up that 5v wire, as it is better to let the LM7805 on the Raduino supply the 5v.
The CP2102 is primarily 3.3v, but the pins are 5v tolerant.
The Nano has 5v TXD/RXD pins.
It works.
