Hardware not found, USB port test gives inverse results.

#1
Hi all, this is my first attempt using a picaxe chip.
I have wired up a circuit as shown (powered using a power supply at 5V) but cannot find the hardware using the programming editor. When I try the usb port test with the multimeter between the input pin and ground the signal is at -0.1V to start with and then goes to high when I switch on the onscreen LED - the opposite to what should happen! Can anyone spot a mistake or a reason why this is happening? The images attached show the setup.


Cheers,
David
 

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Janne

Senior Member
#2
Hi,

Looking into the picture one thing comes to my mind.. Make sure the wires you have soldered to the 3.5mm socket connect to both parallel legs. The other leg disconnects when the plug is inserted, and if the wire is only soldered to that one it will cause great frustration when trying a download.
 

Goeytex

Senior Member
#3
You have the wrong adapter. The XH8290 does not invert the serial data as required.

Look in Device Manager under Ports ( Com and LPT) and tell us what driver is loaded for this com port. It will likely be either PL2303 ( Prolific), CP2102 (Silabs), or FTDI.
If it is Not FTDI then the only way to make it work is to add components on the board to invert the serial data lines.
 

Janne

Senior Member
#4
You have the wrong adapter. The XH8290 does not invert the serial data as required.

Look in Device Manager under Ports ( Com and LPT) and tell us what driver is loaded for this com port. It will likely be either PL2303 ( Prolific), CP2102 (Silabs), or FTDI.
If it is Not FTDI then the only way to make it work is to add components on the board to invert the serial data lines.
Isn't the XH8290 just a regular USB to RS232 adapter? Then it should work, after all that's how picaxe was originally programmed with the AXE026 cable. And I've programmed picaxe's with other usb to serial adapters + axe026 cable too in the past..
 
#5
With RS232, a "0" is represented by a positive voltage in the range 3 to 25 volts but more likely between 5 and 15 volts.
A "1" by specs is a negative voltage of the same magnitude however a bit of equipment would accept zero volts.
The PIC chips by their ESD diodes will hold any negative voltage to around -0.3 volts .

Hence by default RS232 has signal inversion.
 

Goeytex

Senior Member
#6
Isn't the XH8290 just a regular USB to RS232 adapter? Then it should work, after all that's how picaxe was originally programmed with the AXE026 cable. And I've programmed picaxe's with other usb to serial adapters + axe026 cable too in the past..
If it is, then why is the OP's data reversed ?
 

hippy

Technical Support
Staff member
#7
RS232 out of a 9-way D would normally be idle low ( <= 0V ) and active high ( > 3V ) which is directly compatible with the PICAXE download interface.

When connected to a passive AXE026 9-way to jack cable, the most likely reason for the voltages to appear inverted would be measuring between the wrong points on the 3.5mm jack.
 

Technical

Technical Support
Staff member
#8
The photo does not show an AXE026 serial cable, it looks like a different brand cable and so may not even be wired the same.
 

Goeytex

Senior Member
#9
The measurement should be take directly across Picaxe Leg 2 and Leg 8 with the negative meter lead on leg 8.

If the wiring is correct and the adapter is a real Dick Smith and not a cheap fake that is missing the max232 chip, then the voltage levels and polarity should be correct.

With the measurement taken at the points noted above, and the polarity still reversed in the test, then it is possible that the yellow and orange wires in the connector are reversed.

With the connector unplugged from the board, measure the voltage between the orange and yellow wires with the meter neg lead on the yellow wire. With the test active and the green LED on, the voltage should be somewhere between +10 and +15V. With the LED OFF, it should be between -10 and -15V. If these are opposite then swap the yellow and orange leads around.
 
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#12
Thanks all for your help! It was in fact an issue with the wiring on the adapter, the ground and serial in were wired around the wrong way on the adapter which I had assumed was the same as specified in the manual.
The circuit is now working successfully, triggering three cameras every 2 seconds simultaneously for a stereo vision project.
Thanks again,
David
 
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