|Don't ask to ask, just ask|
Re^5: Win32::SerialPort v. New computersby afoken (Monsignor)
|on Nov 03, 2011 at 13:06 UTC||Need Help??|
The device becomes a different COM ports on different computers (e.g. COM6, COM11).
Well-known behaviour of most USB-to-RS232 adapters with Windows. It depends on the available internal COM ports (based on 8250 / 16450 / 16550 and clones), the virtual COM ports that once were used (e.g. by other USB-to-RS232 adapters or Bluetooth devices), and sometimes even on the actual USB port into which you plug the adapter. Someone at Microsoft must have decided that it is a good idea to reserve COM ports for devices that had been plugged in ages ago.
This particular imported no-name USB->RS-232 device was based on the Prolific (a Taiwanese company) PL-2303 chips, as I suspect many commercially available models are. Use the install software that comes with the device - NOT a generic driver from Prolific. Make sure the device says it supports Windows 7 if that's what you're going to use it on. I installed it successfully on one XP computer using the device manufacurer's software. When I tried in on another XP computer using Prolific's generic sofware from their website - it failed miserably. Reboot after installing -even if it doesn't tell you to do so.
There seem to be two different kinds of such adapters. Some identify as a generic RS232 adapter and are supported out-of-the-box by the drivers that came with Windows. And the other ones need vendor- or chipset-specific drivers. I would try to avoid the second type, because no vendor spends much money on testing the driver software for a device that costs less than 6 €. Most vendor drivers seem to be rebranded chipset drivers from the chipset manufacturer.
Note that Linux handles USB-to-RS232-adapters a little bit different: The first free device name is assigned, typically /dev/ttyUSB0 for the first adapter, /dev/ttyUSB1 for the second one, and so on. No reserved devices. Unless you configure udev to identify a certain adapter by its vendor and device ID and its serial number and to assign it a constant device name. Other adapters will still get the first free device name.
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)