QD2 Reset pin floating high after activation

[CarlFST60L_3rd]

I am having an issue with PTA5 floating high after it has been activated.

Here is the very simple experiment I perform to cause the processor to latch up or float PTA5:

Software is basically doing this (just to give an idea):

SOPT1 = 0x00   //Cop off, disable BDM
ICSC1 = 0;     //Clock setup
ICSC2 = 0;
PTA0 = input
PTA1 = input
PTA2 = input
PTA4 = output
PTA5 = input
while(1){}


Now, for hardware, I just have a 100K pull down on PTA5. PTA5 is 0V on power up as expected. If I then pull PTA5 to 3.3V, it stays floating around 2V once I release the 3.3V. I can get it to go back to 0V by shorting it, or using a low value pull down resistor. If I do this on say PTA1, the input goes back to 0V as expected.

I have found this to be the only hint in the data sheet that this pin requires something 'special', from page 18:
"6 - PTA5 does not contain a clamp diode to VDD and should not be driven above VDD. The voltage measured on this pin when
internal pullup is enabled may be as low as VDD – 0.7 V. The internal gates connected to this pin are pulled to VDD."

I also have a more complex experiment which causes this same float state when powered up with PTA2 pulled to 5V via a 470K resistor, but, only PTA2, non of the other inputs cause this to happen.

Thanks in advance.
Carl.

Edit: using Code warrior 5.0.9, and the processor is a S08QD2 8 pin SOIC running 3.3V


Message Edited by CarlFST60L_3rd on 2008-07-30 05:26 AM

Message Edited by CarlFST60L_3rd on 2008-07-30 05:27 AM

Message Edited by CarlFST60L_3rd on 2008-07-30 05:31 AM

Message Edited by CarlFST60L_3rd on 2008-07-30 05:40 AM

Message Edited by CarlFST60L_3rd on 2008-07-30 05:51 AM

[bigmac]

Hello Carl,

Are you certain that the internal pullup is not enabled on PTA5?  Perhaps you have enabled either the IRQ or the KBI module for that pin.  If so, you would have a voltage divider between the internal pullup and the external pulldown resistor.

This might explain what you are observing.

Regards,

Mac

[CarlFST60L_3rd]

Hi Bigmac,

I am certain, the code is literally only SOPT1 = 0x00 and thats it. And it does it every time.

Its like the pull up just turns on when I pull the pin up, then turns off when I pull it low. I have tried this on several chips out of a tube, they all do it with SOPT1 = 0x00 and pretty much no other code.

[CarlFST60L_3rd]

After more playing around, it appears that the requirments to pull this pin down are quite different to anything I have used or seen before on any freescale processor I have used, or what is specified in the data sheets.

Who do I talk to about getting a specification on PTA5? Why wont a 100K pull down allow the pin to return to a low state after going high when all others will?


Message Edited by CarlFST60L_3rd on 2008-07-30 06:23 AM