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Fails to connect via USB-Serial-RJ25 Cable 
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Joined: Sat Nov 19, 2011 9:55 am
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Post Fails to connect via USB-Serial-RJ25 Cable
Good morning....hopefully someone can point me in the right direction here.

I'm a tech for our school and trying to help our Robotics teacher out with a problem with RobotC for VEX. We have 6 Windows XP SP3 laptops and 6 sets of cortex/joysticks. We have 1 set that works perfectly but have a lot of problems with all the others as follows:

- firmware for cortex and joystick downloaded and updated on all devices via USB-USB cable without any problems
- cortex and joysticks 'paired' via vexnet and working (tested by attaching motors and the joysticks control them)
- robotc firmware download via the usb-serial-rj25 cable has only worked on 1 device (set 1)
- all other devices, no matter which laptop used fail just telling me to check batteries, check connections etc etc

I've reinstalled all the software and drivers on one laptop and same result....I've reinstalled windows on another laptop so everything was fresh and same result.

- set 1 (the one which worked) will connect via that cable from ANY laptop and can download programs etc - but the other 5 sets will not work on any laptop at all

As far as I can tell it HAS to be something with the cortex/joysticks as that one set that works works on any laptop so the software and drivers are working fine.

I've followed the instructions and videos to update firmware and configure joystick etc numerous times and everything works until it needs to use that usb-serial-rj25 cable in the program port on the joystick.

Has anyone else seen this and if so did anyone have a solution as the club as a competition in a week or 2 so really need this working and I am stuck.


Sat Nov 19, 2011 10:03 am
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Joined: Tue May 15, 2007 9:02 am
Posts: 405
Post Re: Fails to connect via USB-Serial-RJ25 Cable
What version of ROBOTC are you using? ROBOTC 3.04 is the latest version - I'd recommend updating if you're using an older version.

If you go to View > Select Communication Port, does the "Prolific USB-to-Serial" option come up as one of the available devices? If it doesn't show up, this indicates that it's not properly communicating with Windows. If it does show up, make sure that it, or the "Automatic Selection" option is selected.

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Jesse Flot
CMU Robotics Academy
ROBOTC Support


Mon Nov 21, 2011 12:29 pm
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Post Re: Fails to connect via USB-Serial-RJ25 Cable
On latest version and yes it does show up as an option. As I said - it works perfectly but only for 1 set of controller/cortex the other 5 sets it does not work on so I do not believe it is the drivers/cable or it would not work at all for any of them.


Mon Nov 21, 2011 12:38 pm
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Post Re: Fails to connect via USB-Serial-RJ25 Cable
You mentioned that the one cable can be used to communicate with any of the sets. Have you tried using the working cable and a working Joystick+Cortex on the other computers? Although unlikely, it may be that the settings are perfectly fine, but you have a bad batch of cables.

I know that you said that you've been able to pair the devices over VEXnet, but you might also use the VEXnet USB keys from the working set to test the other sets. We have seen a number of these go bad where they will progressively fail - they might be OK for a while with remote control, but are no longer reliable enough for downloading firmware.

Keep in mind as a backup that you can download ROBOTC firmware and programs over the USB connection, then unplug the USB and swap in the VEXnet Keys to do remote control.

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Jesse Flot
CMU Robotics Academy
ROBOTC Support


Mon Nov 21, 2011 12:49 pm
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Post Re: Fails to connect via USB-Serial-RJ25 Cable
We only have, to my knowledge, one of the USB-Serial and USB-USB cables...or at least that is all I have been given by the Robotics teacher. So we have one set of cables and six sets of laptops and associated joysticks/cortex.

#1 is the set that works.

I plugged #1 into laptop #6 with the USB-Serial cable and it downloaded a program to the cortex perfectly without any problems - so the working cable AND working devices will work on any laptop.

I swapped the vexnet keys from #6 devices to #1 and it still worked fine - testing the vexnet from #1 in #6 devices I was able to run an attached motor so it appears the vexnet keys are working fine.

I was able to download the RobotC firmware and a sample program to #6 using straight USB so I guess that is working and will test on the other sets - any idea though why the USB-Serial would not work on most of them?


Mon Nov 21, 2011 1:13 pm
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Joined: Tue May 15, 2007 9:02 am
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Post Re: Fails to connect via USB-Serial-RJ25 Cable
Sorry, I'm out of ideas. The folks at VEX support and maintain the driver for the cable. You might contact them for some additional input: http://www.vexrobotics.com/contact/contact

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Jesse Flot
CMU Robotics Academy
ROBOTC Support


Mon Nov 21, 2011 1:18 pm
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