varying com ports

have three uno boards here - using same usb port and cable, winxp device manager cpu a gives on uno#1 "uno com4" , uno#2 gives " uno com3" and uno#3 gives "usb device" while cpu b gives uno#1 "uno com4" , uno#2 gives "uno" and uno#3 gives "usb device" - why differing com ports ? why sometimes no com at all ? where is the documentation ?

update: so now have three uno boards - one goes to com3 one to com4 and one to com6 - what's with that ? how do u get all three uno boards talking to the same com port ? where is the documentation hidden ?

russw4ni: update: so now have three uno boards - one goes to com3 one to com4 and one to com6 - what's with that ? how do u get all three uno boards talking to the same com port ? where is the documentation hidden ?

It's not an arduino thing, it's an operating system USB device detection thing. Each arduino on-board USB serial converter chip has a unique identifying number so that when it's first plugged into a PC it assigns it the next new serial port number available. I think I'm up to 12 or more different comm ports assigned to the FTDI chips on as many boards.

Having said that, there has been posted in this forum a way to go into device manager (for windows at least) and manually reassign any given 'arduino device' to a specific comm port number, I just don't have a link as I've never thought it to be important enough to do.

Lefty