DIY 'AXE027' problem

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GrahamGo

Senior Member
Periodically I get a problem with the AXE027 cable.

In Picaxe Programming Editor - Options - Serial Port. see COM2 (not available) AXE027 PICAXE USB. When I click on "Scan for USB Cable" it says "An AXE027 Download Cable is connected to Com2 but is being used by another application". Close the application using COM2 to use the cable for program downloads.

I have tried rebooting the PC, re-installing the AXE27 driver, but I keep getting the above message.

How can I see which application it thinks is claiming Port2 and are there any tricks to force things COM2 back to normal?

Cheers.
 
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inglewoodpete

Senior Member
More information

I don't know the answer but can you answer the following questions? I suspect that the answer will halp diagnose the problem (or eliminate some dead-ends).
  • Which operating system are you using?
  • Does the computer use bluetooth?
Posts from #38 on this thread may help.
 
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mrburnette

Senior Member
It is somewhat rare for a USB device to assume COM2 since COM1/2 are usually reserved for physical serial ports. That being said, 16550 UARTs can map to COM1/COM2 to support virtual modems, etc. We often see that as the OS evolves from XP --> Vista --> Win7 that visualization is ever more common place. Bluetooth stacks can also remap into the old physical port/interrupt ranges to support serial over Bluetooth.

MSInfo (msinfo32.exe) is commonly found on Microsoft installations and can give you some insight into the PORTS and Interrupts usage... especially helpful under XP.

- Ray
 
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GrahamGo

Senior Member
Hi, Thanks for the input Its a recent clean install of Windows 7 32bit. I do sometimes use Bluetooth, but on this fresh install I haven't installed the Bluetooth drivers yet.

As to the other reply @Mrburnette. Ray, I have disabled the Communications port (COM1) and the ECP Printer port (LPT1) in device manager, I also changed the AXE027 to COM2 in the device manager - advanced settings section.

Its weird, the PC just seems to get into a mood, and insist's that COM2 is already being used by another program. Even if I turn the PC off, pull the power plug and leave it for a few minutes. Power up and it's back in its moody mode. But most of the time the PC is happy and gives me COM2..... At all times plugging the AXE027 in and out gives the normal ding dong, dong ding sound.

I just tried MSinfo32 in the CMD window. I see -components - Ports - serial and parallel is blank (empty). In USB I just see Intel(r) 5x entries with long numbers. In Problem devices I see COM1 and LPT1 - disabled

But right now the PC is in happy mode and AXE027 is working.....
 
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caseybee

New Member
I have come to the conclusion that the message is incorrectly worded. I periodically get this message. it seems to depend on the sequence of events switching on/ switching off that causes it. I have not worked out the correct sequence of power to AXE091, connect AXE027 to AXE091, connect AXE027 to PC, load PE. A few minutes plugging in and out etc gets it working.
 
hippy

hippy

Ex-Staff (retired)
GrahamGo said:
I have disabled the Communications port (COM1) and the ECP Printer port (LPT1) in device manager, I also changed the AXE027 to COM2 in the device manager - advanced settings section.
Click to expand...
That may be part of the problem. As Ray says; COM1/2 are legacy devices which might be handled by Windows in a different way to other serial ports. Try with the AXE027 set as something higher than COM2 and see if you have better luck with that.
 
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GrahamGo

Senior Member
Thanks that's a good point, I will change the COM2 to something different. Now I am wondering which port the AXE027 selects by default.
 
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GrahamGo

Senior Member
Problem fixed.

Changed to COM: 5 - but the problems persisted.
In Device manager removed drivers etc and re installed the AXE027 drivers, it chose COM: 3 - but problem persisted

Finally an inspiration moment. I have an 08M2 programmed as I2C master, sending various test packets to my slave target 14M2. The 08M2 is powered all the time, the 14M2 is connected to the AXE027 and is powered via a momentary switch to supply the reset. The problem was that the 08M2, either the data or supply voltage on the SDA SCL lines was corrupting the 14M2 sufficiently that it was sometimes not resetting.

I still don't understand why, because the I2C pullups where being powered down via the momentary switch and I thought the 08M's I2C lines are passive and needed the pullup's. Anyway I moved the 08M so that it was powered off with the switch, and introduced a 5 second delay before it transmits the i2C packets. - lesson learned.

Thanks for the input.
 
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papaof2

Senior Member
The 14M2 won't be truly powered off unless ALL sources of power are removed. Because of the protection diodes on many of the chip inputs, the pullups on the SDA and SCL lines *could* be providing (limited) phantom power to the 14M2 and causing it to be in an unpredictable state.
 
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GrahamGo

Senior Member
Finally found the real reason for the "COMx unavailable" problem. It is finally fixed. For simplicity I have been referring to the AXE027 interface. but in reality I am using the MM232R USB module from FTDI. This uses the exact same chip as the AXE027. I used the FTDI editor to change the MM232R's flash settings Vendor:- unchanged at 0403, Prod ID changed from the default 6001 to BD90. With pins 6 & 8 linked this module is now recognized by the Picaxe software as being a real AXE027 physical device. So far so good. Everything works except the problem I described in this thread.

Anyway I found a subtle difference. This is that on the AXE027 module the TX and RX lines have a 180 ohm in series and a 10k ohm to ground. The MM232R does not, and this is the key. Sometimes, and I don't know why, the RXD line into the MM232R supplies a very weak 3.3vdc. Without the 10k pull down this sits at about 1.2v on my 14M2's TX pin. This is sufficient voltage to do something to the 14M2 and/or USB serial connection that causes the COM port to become unavailable.

If I install a 10k pull down resistor the voltage drops to 0.1vdc, so its all voltage and very little current capability, but hey presto, the problem is gone.

Conclusion. The USB FT232RQ chip is very popular and you may, like me, might not be using a pucker AXE027. Do change the Prod Id if you wish which allows the normal AXE027 driver to recognize the hardware. But more importantly install the extra resistors if they are not present. then life gets more predictable....
 
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GrahamGo

Senior Member
MartinM57 said:
Well done - good debugging :)

Your first post...

...in hindsight, it might have been better have been a bit more accurate maybe
Click to expand...
Yes, sort of bit me that one! But I was pretty convinced it was a W7 driver problem, I knew that I was using the same FT232RQ and it was configured as per the AXE027, so I called it an AXE027. As the 14M2 Rx already has a 10k pull down and 20k in series. it boils down to a single missing resistor. I found the AXE027 schematic at the very bottom of the PDF. No excuses, but I discounted the - ahem "AXE027" too soon. The fact that unplugging and re-plugging the USB cable often fixed the problem sort of re-enforced my conviction as to where the problem was. Anyway it turned out to be a good ending and perhaps the posting helps others using other USB adapter variants. Lesson learned!
 
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srnet

Senior Member
Not really very fair on Rev Ed either.

The title of the thread is in big bold letters "AXE027 problem"

And not a problem with one of their products at all so might be an idea to edit the first post to clarify.

At least you owned up though.
 
hippy

hippy

Ex-Staff (retired)
I've edited the title of the thread appropriately.

It's always best to have full disclosure at the start otherwise people can go in the wrong direction, wasting time investigating things which are not an actual problem, and of course it does nothing to solve the problem there is.

Had it been said it was a clone AXE027 the first question would likely have been; how do things behave with a genuine AXE027 ? That could quickly lead to asking what's different about the hardware ?

Anyway, problem solved.
 
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GrahamGo

Senior Member
hippy said:
I've edited the title of the thread appropriately.

It's always best to have full disclosure at the start otherwise people can go in the wrong direction, wasting time investigating things which are not an actual problem, and of course it does nothing to solve the problem there is.

Had it been said it was a clone AXE027 the first question would likely have been; how do things behave with a genuine AXE027 ? That could quickly lead to asking what's different about the hardware ?

Anyway, problem solved.
Click to expand...
Totally agree, and thanks for changing the title. That item did trouble me. Here is my original thread about the clone AXE027. That thread is correct, except for the missing resistors. I will edit that thread - sorry for misleading, there was no intention to do that at all.

http://www.picaxeforum.co.uk/showthread.php?20202-AXE027-USB-clone&p=192303#post192303 post#4
 
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