/dev/ttyUSB0 and /dev/ttySer0 are the same. /dev/ttySer0 is a symbolic link to /dev/ttyUSB0. When a device gets connected to the USB port a UDEV rule automatically creates a symbolic link.
As for the problems with the serial communication it could be a number of things. The fact that the higher baud rates work says that the timing between the two devices are within tolerance. Clock speed differences can cause some errors with RS232 or 485.
Have you tried a different cable? How is the cable wired? is it a straight through cable or a Null Modem cable. If you have access to an oscilloscope you can check for signal integrity and timing. It could be some funky issues with signal grounding as well. Is the RIO power supply grounded?
standard serial cable with null model adapter between. all of the typical serial issues I would expect to be worse at high speed… power supply is grounded and connected to same outlet as the laptop.
I guess i will scope the communication while waiting for the “approved” adaptor
I have a 9600 baud power meter hooked up for over a year and have never seen any issues.
I recall testing some 300 baud gear that a customer supplied way back in the early RIO days and never had a hint of a problem there…
Also this is the first time hearing about this sort of problem. I will ask around some, but suspect that its something going on locally as @reevesjj suggests vs an issue with Node-RED or RIO.
I have to admit, it sounds odd that it works on the laptop, but not on the RIO, but suspect a ground loop is offsetting things.
PL2303 based devices don’t work at all since they have -11v/+2v signal
I expect these deficiencies are exacerbated by going adaptor-adaptor, instead of typical usage of connecting to a piece of equipment. It could be they are relying on the other receiver to help pull signal up to +5v.
I probably wouldn’t notice this if I installed directly instead of trying to setup a simulation at the desk first…
Yeah the RS232 standard +3 to +15 volts is a 0 (mark) and -3 to -15 volts is a 1 (space): You were barely out of spec on a pretty generous voltage range. It looks like there is an issue with how the PL2303 devices was trying to bias it’s circuit to common. I am willing to bet it has something with the charge pump circuit in the adapters expecting a real ground somewhere. I wander if you bind the pin 5 of the DB9 cable to chassis ground if it would improve things.
