USB to serial (RS-232) adaptors all different?

[JPrevost]

So I've got hardware (as many of you know) that just streams data straight to the serial port and the PC datalogs it... trouble comes when using USB to serial adaptors. I've got 2 to experiment with, one is a Radio Shack brand, the other is Belkin. The Radio Shack adaptor crashs the whole computer system if you close the serial port while it's recieving from the hardware. This is very frustrating and from a friend, it seems to be a driver problem. Something I can't control . To get around this I've been trying to read all of the bytes waiting at the port and then quickly closing the port. So far it's been good. Only 20% crashing. Now with the Belkin I've got a whole nother problem. It doesn't want to drop any of the data. For example, even if I don't want to datalog, it backlogs into some hidden buffer! I'm thinking the only way to work around this "hidden buffer" is to read all of the bytes at the port, flush it, restart. Do this every time the user starts and stops the datalogging. So now, to make my life even harder, I've gotta look at the USB device name and figure out which device is being used. Anybody else having these issues and if so, how are you handling them?

[Yair]

Now with the Belkin I've got a whole nother problem. It doesn't want to drop any of the data. For example, even if I don't want to datalog, it backlogs into some hidden buffer!

I have seen something similar, where while talking to the device I would get rubbish and even after disconnecting the device, I still kept getting an answer from the port.

What was needed in that case was to go into the windows device manager and properly configure the port number to talk to the "real" virtual serial port and not to the fake one (although I don't remember exactly how at the moment, but it shouldn't be complicated).

[Rolf Kalbermatter]

So I've got hardware (as many of you know) that just streams data straight to the serial port and the PC datalogs it... trouble comes when using USB to serial adaptors. I've got 2 to experiment with, one is a Radio Shack brand, the other is Belkin. The Radio Shack adaptor crashs the whole computer system if you close the serial port while it's recieving from the hardware. This is very frustrating and from a friend, it seems to be a driver problem. Something I can't control . To get around this I've been trying to read all of the bytes waiting at the port and then quickly closing the port. So far it's been good. Only 20% crashing. Now with the Belkin I've got a whole nother problem. It doesn't want to drop any of the data. For example, even if I don't want to datalog, it backlogs into some hidden buffer! I'm thinking the only way to work around this "hidden buffer" is to read all of the bytes at the port, flush it, restart. Do this every time the user starts and stops the datalogging. So now, to make my life even harder, I've gotta look at the USB device name and figure out which device is being used. Anybody else having these issues and if so, how are you handling them?

USB really isn't something you should use when you want to rely on it that it runs for weeks uninterrupted. While the idea of USB is nice there are a myriad of things which can and often do go wrong.

The first and most obvious problem are the devices itself. There are many USB chip solutions out there that have simply more or less grave bugs in the silicon. They are sometimes getting fixed in later versions of that chip, if the manufacturer actually cares enough to fix its silicon instead of just releasing yet another silicon design with new bugs in there. Then the device drivers of those devices, quite often they are more or less taken over entirely from the development kit of the silicon manufacturer despite of notices all over the place that the software is only provided as an example of how it works and shouldn't be used in production quality designs.

Then a quite common problem too are the actual USB chip bridges in the PC themselves and the according drivers. Nowadays those PCs are designed in a matter of months and often the newest chips are used despite that they have sometimes bugs too and their drivers are not yet mature. Maybe it is possible to patch the problems later on with a driver update and maybe the bug is not really fixable in software, which with most PC manufacturers nowadyas means bad luck for the end user.

Basically if you want to use USB for uninterrupted long term data acquisition you will have to evaluate both the data acquisition hardware as well as your PC platform very carefully before doing so. USB for life supporting devices is definitely something you should never attempt to do unless you fully control the entire chain from controller software and hardware to the device software and hardware.

Rolf Kalbermatter

[i2dx]

i had some trouble with an USB to serial adapter, too, this week (keyspan 19Hs). but the reason was not the adapter, but the USB 2.0 Hub (a cheap one from the supermarket ...): the voltage controler got to hot and the hub "hang up" ...

after applying a heatsink, all worked fine ...

[Karl Rony]

My company standardized on IBM desktops and laptops with one or no serial ports. The desktops only supply two standard PCI slots and I've filled them up. Thus, I've moved to USB serial adapters.

I stumbled upon www.byterunner.com as a supplier. I've had terrible experiences with the 2 port version based on the FDDI chipset. My LabVIEW application didn't work reliably and neither did my AutomationDirect PLC programming application. However, I am successful with the single port version using the Prolific chipset.