still trying to upload to a 08M

[nickwest]

Greetings folks, this seems a bit dim but I've run out of things to tweak. I am trying to download a simple test program from a winXP desktop, (using version 4.1.17 of the program editor) to a PICaxe 08M. I'm using the simple two-resistor download circuit, and I keep getting the "subscript out of range" error. I've tried running the PICaxe on four fully-charged NIMH AA batteries (which I measured at 5.5V), but after reading some other threads I'm now using three cells which gives me about 4.3V. I've tried the "test" feature under View>>Options>>Serial Port (that screen with the big green LED you click on). When the clickable LED is off (dark green) the input pin is at about 3.9V. When the LED is on (light green), the voltage increases to about 4.8V. This is incorrect but there is at least a change.

I've also tried putting an LED across the serial output pins of the PICaxe, just to see what's going on. I get a dim glow while ever the serial cable is connected, then when I attempt to send a program to the picaxe I get a brief flash from the LED then it goes dark until the evil subscript out of range error comes up.

So I'm out of ideas until I can find another PC with a serial port to test this thing on, unless anybody can suggest something else I might try.

I even tried another 08M that I'd ordered at the same time. Unless there was a dodgy batch I can't imagine they are BOTH broken from the factory, it has to be something stupid I'm missing, but what? Any suggestions from the picaxe community would be welcome at this stage. If I'm not explaining things correctly please let me know and I'll try to clarify!

 

[hippy]

I suspect the problem is not with the PICAXE but with the serial port or your interface wiring. Check that you don't have any shorts, have the download circuit correct, and haven't accidentally pulled the input line to +V rather than down to 0V.

Particularly check that you haven't inadvertently crossed over the PC's RX and TX lines.

With the PICAXE-08M removed from the circuit, when the PC is not sending data to the PICAXE Leg 2 should show near 0V, and may even be negative, and when sending it should go up towards +5V/+12V.

Not sure what the "Test" function for a serial port does, but you could try using the "Firmware?" button ( also under View-Options ) and the voltage should briefly jump from 0V/-Ve to +5V/+12V, the LED flashing from off to on.

With the Programming Editor Terminal (F8), the LED should also be off and flash as characters are sent. You don't need the PICAXE connected to allow data to be sent.

You can also look at the voltage on the PC cable when not connected to the PICAXE. It will more often than not be be 0V/-12V when not sending, and +5V/+12V when sending.

Edited by - hippy on 21/06/2006 15:22:46

 

[Technical]

The LED on the test function clears and sets the serial port break condition, which therefore switches the RS232 serial transmit pin high and low. So you should get a roughly 0 to 4.3V change on the serial input pin of the PICAXE when you click the LED.

The voltages you are seeing indicate incorrectly setup hardware - check the 10k/22k resistors carefully.

 

[nickwest]

Well folks, thanks for your responses. I tried tried downloading from a different PC. This time I could get firmware info but not actually send a program across. (memory verification failed)

I then gave ethe circuit a vigorous poking and the LED connected across the serial input pin, which had been lit dimly whenever the serial cable was connected, went out. Now my programs upload fine.

So I think it was just just a dodgy ground going to the picaxe. Interesting though that it didn't completely sever communication to/from the PC - as I said the firmware check worked fine!

Thanks again for the assistance!