The situation with the FTDI chips is rather complicated - the early ones had an optional external serial EEPROM that you could use to change the device defaults - this was mostly used for changing the VID, PID and device description string but if you put a serial number in there it's reported to the driver - so if you don't get a serial number then it either means that the EEPROM isn't fitted or that it hasn't been programmed.
On a lot of the more modern chips, the EEPROM (or "MTP memory" in FTDI speak) is built into the device and hence is always available - but may not have a serial number stored in it. If you have a device that has the EEPROM installed but no serial number you can set one yourself using the FTDI Mprog or FT_Prog software. The Prolific chips also have support for a serial number, but I don't think I've ever seen a device that implements it - my guess is that this is because the external EEPROM needed costs nearly as much as a PL2303 does, and those Prolific chips tend to end up in price sensitive applications. On Mon, Jan 28, 2013 at 4:50 AM, Hal Murray <[email protected]> wrote: > > [email protected] said: > > FTDI devices with their device driver should remember the COM port they > > have been assigned on an individual system even if they get plugged into > a > > different port/hub, and this greatly reduces reconfiguration effort if > you > > change any USB connections - Other manufacturer's devices have a > tendency > > to use a new COM port number each time they are plugged into a different > > physical USB port connected to the same computer. > > The USB protocol has provisions for each device to provide a SerialNumber. > That lets the OS connect them up at the appropriate logical name no matter > which physical port they are plugged into. They have been common on disks > and thumb drives for a long time. My printer has one. So does my scope. > > Most low cost USB serial adapters don't (or didn't) have a useful serial > number. (Or maybe the Linux drivers don't use it, but I suspect that's > done > at a higher level so it should work for serial if it works at all.) > > I have some FTDI adapters that produce useful serial numbers. > usb 3-1: SerialNumber: A4003UAg > usb 5-2: SerialNumber: A4001h2X > I'm pretty sure I have other FTDI ones without a serial number. > > I don't think I've seen a useful serial number on any Prolific gizmos. My > collection includes lots of older gear so my sample may be biased and/or > things could have changed. > > It might be helpful to collect a list of which gear from which sellers > do/don't have useful serial numbers. > > With Linux, the udev stuff will let you setup a /dev/xxx alias when it > sees a > particular serial number. I'll say more if anybody wants. > > > > -- > These are my opinions. I hate spam. > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
