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Topic: Mega 2560 Detection Problems (Read 1 time) previous topic - next topic


Hello everyone,

I just recently purchased an Arduino Mega 2560.  It has been working for the past several days, but yesterday I was unable to program it (I'm sorry to say I did not write down the error code and can't get it back).  At this point, the Mega is detected by Windows 7 64 bit in device manager, and is assigned a COM Port number (COM5).  However, the COM port does not appear on the Arduino Tools menu.  COM 3 and 4 appear in the Tools menu, but COM3 does not appear in Device Manager (COM4 is one of the computer's internal ports). 

The Mega itself seems to be working fine, my last sketch still runs perfectly (Using an Adafruit 2.8" TFT LCD shield w/ Touchscreen).  The last time I was able to program it the shield was attached (though I had done this several times before with no problems).  Could that have caused my problem? 

I read several posts from people with similar issues, and have tried reinstalling the Mega drivers with no success.  The only other changes I have made is I was using a different version of the rxtxSerial.dll file, because the version that came with the Arduino environment takes about 30s to open the tools menu on my computer (the custom rxtxSerial.dll file had fixed this issue).  I took a new copy of the original file and placed it in my Arduino folder, but it did not resolve the issue.  I have an Arduino Uno which is working perfectly, so I am assuming the USB cable/USB Port/Arduino Environment are all working.

Any ideas?

Thanks, Brendan


Hmmm....  the rxtx library and DLL are the things that determine which COM ports appear in the menu, so I'd start there.  Can you get rid of the custom RXTX DLL and try with the standard one? 

Also, make sure there aren't any other programs trying to scan / use COM ports (e.g. for things like cellular wifi dongles, cellphone syncing, etc). 



I did try replacing the rxtx dll file with the original from the Arduino zip package with no luck (the UNO still works fine by the way).  Maybe it would be worth it for me to do a complete reinstall.  I will try looking for software running in the background that could affect the COM Ports, and if that doesn't work I'll try a new installation. 

Will post results this afternoon. 



Life is good.

I tried using my Mega 2560 with an older version of Arduino with the same results (Arduino did not list the COM Port it was connected to, even though Windows detected it).  I then tried a Mega ADK which I had, and was able to reproduce the error message that showed up before all my problems started.  The error message (for anyone who finds this post by way of Google) is:

avrdude: stk500v2_command(): unknown status 0xc8
avrdude: initialization failed, rc=-1
         Double check connections and try again, or use -F to override
         this check.

avrdude: stk500v2_command(): unknown status 0x01
avrdude: stk500v2_disable(): failed to leave programming mode

I had more luck looking for programs running in the background that may affect the COM Port.  The first I found was my laptop's Bluetooth radio (I remember reading somewhere that this could cause a delay in Arduino when opening the "Tools" menu).  The second program was Tera Term, which is a terminal emulator which apparently runs in the background.  The third was PDANet (I don't know if it affects the COM Port or not, but scans for a cell phone on the USB port). I disabled all three programs and now the Mega boards are working fine.  In addition, one of these three programs must have been affecting the time it took the "Tools" menu to open, because it opens instantly now. 

I find it very interesting that the UNO was still working fine even though the Mega was not working (this musing is again for the benefit of visitors from Google).

Thanks everyone for your help.   

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