[time-nuts] Serial port / Mouse issue (was mentioned in"Thunderbolt Monitor")

Peter Bell bell.peter at gmail.com
Mon Jan 28 01:25:18 UTC 2013


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 <hmurray at megapathdsl.net> wrote:

>
> stephen at tompsett.net 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 -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>



More information about the Time-nuts_lists.febo.com mailing list